Crookes, William

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Crookes, William

(b. London, England, 17 June 1832; d. London, 4 April 1919)

chemistry, physics.

Crookes was the eldest son of the sixteen children of Joseph Crookes, a prosperous tailor, by his second wife, Mary Scott. In 1848, after irregular schooling, he received his scholarly introduction to science when he became a student at A. W. Hofmann’s Royal College of Chemistry in London. After gaining the Ashburton Scholarship, he served as Hofmann’s personal assistant from 1850 to 1854 and came to the attention of Faraday at the Royal Institution. Faraday introduced him to Charles Wheatstone and George Stokes, and together the three men were largely responsible for turning Crookes away from traditional chemical problems and toward chemical physics, exemplified then by the optical problems of photography and later by spectroscopy. There are many indications that Crookes consciously modeled himself on Faraday, with whom he shared a brilliant experimental and lecturing ability, a scrupulous orderliness, and an ignorance of mathematics. This ignorance, however, was often masked in later years through his friendship with Stokes, who privately solved many mathematical problems in physics for him. Nevertheless, the rigorous training in analytical techniques that he received under Hofmann remained the foundation for all of Crookes’s subsequent researches and his commercial activities. In 1854, through Wheatstone’s influence, he became superintendent of the meteorological department of the Radcliffe (Astronomical) Observatory at Oxford; and in 1855 he taught chemistry at the College of Science at Chester. Finally, in 1856 he settled in London, where, apart from extensive traveling on business, he attempted to bring his name before the scientific community both as a freelance chemical consultant (using a home laboratory) and as an editor of several photographic and scientific journals. He was nominal editor, and proprietor, of the most successful and important of these journals, Chemical News, from its founding in December 1859 until his death. He was knighted in 1897 and received the Order of Merit in 1910.

Crookes married Ellen Humphry of Darlington in 1856; and the necessity of supporting ten children helps to explain the amazing diversity and catholicity of his scientific interests, many of which were frankly motivated by the belief that all pure scientific researches would lead to financial rewards. Unlike Faraday, he was intensely ambitious, both in science and in business. In the latter world he drove many hard bargains; but although he was able to make a comfortable living from such commercial ventures as the sodium amalgamation process for gold extraction, the utilization of sewage and animal refuse, and electric lighting, none of them was financially very successful.

Crookes was an experimentalist of consummate skill, and the brilliance of his experimentation was the dominant feature in his scientific career; his success in producing a vacuum of the order of one millionth of an atmosphere made possible the discovery of X rays and the electron. With fame, honors, and responsibilities to various scientific societies, he was fortunate to be able to leave the experimental side of his researches to equally adept assistants, notably Charles H. Gimingham from 1870 to 1882 and James H. Gardiner from 1882 to 1919. To the latter must be attributed the impressive bulk of Crookes’s researches in his later years, including work on scandium and on “Crookes lenses,” published when he was over eighty.1 From the 1870’s Crookes’s papers ceased to be entirely experimental; and with great effect he used various scientific platforms to offer speculations and to make theoretical pronouncements that, although frequently wide of the mark, were nonetheless plausible and stimulating. He was a great syncretist of other scientists’ hints and suggestions; and by weaving these together imaginatively with the aid of his literary adviser, Alice Bird, Crookes acquired a well-deserved reputation as a Victorian sage.

Sages often have to face censorious criticism during their lifetimes. The most controversial aspect of Crookes’s career, even today, is his investigation “into the Phenomena called Spiritual” during the 1870’s. Following Darwinism it fell to Crookes to provoke the last major eruption in the battle between science and religion. Some critics, notably Crookes’s archenemy, W. B. Carpenter, argued that there were two Crookeses, one a rational scientist.2 Today, with our better understanding of the Victorian mind and of the way in which religion and metaphysics have played a creative role in the scientific lives of men like Newton, it causes no surprise that occult phenomena should have involved the attentions of a major nineteenth-century scientist.

By 1860 Spiritualism was a well-established religion spread, by the grapevine of domestic servants, through all levels of Victorian society. In 1867, following the death of a brother to whom he was devoted, Crookes (who had been brought up with the Christian belief in an afterlife) was persuaded by the electrician and Spiritualist C. F. Varley to attend séances. He became deeply interested in the kinetic, audible, and luminous phenomena that could be witnessed at the fashionable séances of the 1870’s and 1880’s; and although, like Tyndall, Huxley, and Carpenter, he remained skeptical and was intolerant of the frequent fraudulent practices that he detected, he was persuaded that in the case of a few mediums, notably the Scottish-American D. D. Home, the astounding phenomena were genuine. In 1870 he subjected Home, in the presence of William Huggins, an astronomer, and Edward William (“Sergeant”) Cox, a lawyer, to a number of tests; and he became personally convinced that Home possessed a “psychic force” that could modify gravity, produce musical effects, and perform other feats unknown to conjurers or scientists. Crookes published accounts of his investigation in his own Quarterly Journal of Science, but the Royal Society rejected his paper on the grounds that the experimental conditions were insufficiently exacting; subsequently, in 1887, when less hysteria surrounded the issue, the Society allowed Crookes to publish some negative observations on the occult force of M. J. Thore.3

Even more sensational was Crookes’s support in 1874 for the young medium Florence Cooke, who materialized a phantom called “Katie King.” Was Crookes so infatuated that he lied? Was he the subject of an appalling confidence trick that, if he ever understood, he was too embarrassed to reveal? Did he suffer delusions? Did he in fact observe paranormal phenomena? Although all these questions have been answered affirmatively by various people, there is no doubt of Crookes’s sincerity, for he staked his scientific reputation on the validity of the phenomena he described.

Crookes made a prodigious number of investigations of mediums between 1870 and 1900 and was undoubtedly the most experienced, if not always the most critical, of all nineteenth-century psychic investigators. He even built a special room in his house so that investigations could be conducted under rigorous conditions. Not surprisingly for one who claimed to be widely read in “Spiritualism, Demonology, Witchcraft, Animal Magnetism, Spiritual Theology, Magic and Medical Psychology in English, French and Latin,” he joined the Society for Psychical Research on its founding in 1882 and was its president in 1897. He also joined Mme. Blavatsky’s Theosophy movement in 1883. Until his wife’s death in 1916 Crookes never believed that spiritualistic seances presented unequivocal evidence that “spirits” were those of human dead.4 He is best described, therefore, as an occultist, a man for whom traditional science left huge areas of creation unexplored. These serious investigations into the occult were never entirely divorced from his public science; and for the historian of science they illuminate his purely scientific writings, particularly those on the radiometer and on inorganic evolution, and clarify some of the more purple patches in his deliberately exhibitionistic speeches to the many societies that chose him as their president.

Like Tyndall and Kekulé, Crookes frequently stressed the role played by imagination in discovery, or by an “inward prescience” in shaping the development of his work. The most logical aspect of this was the critical appraisal of “finger posts” that were erected by “anomalous residual phenomena.” 5 In this manner Crookes saw a logical sequence running through his work from selenium through thallium, the radiometer, cathode rays, and the rare earth elements to radioactivity.

In 1850, under Hofmann’s direction, Crookes made a routine study of the selenocyanides, using selenium ores from Germany. During the next decade, inspired by Wheatstone, he worked enthusiastically on the new subject of photography, investigating the spectral sensitivity of the wet collodion process; attempting to apply photography to the scientific recording of polarization, astronomical objects, and spectra; and, in 1854, devising the first dry collodion process with John Spiller.

His analysis of the optical sensitivity of photographic processes caused Crookes to speculate privately on the origin of spectra; when the solution was published by Bunsen and Kirchhoff in 1860, and they announced the discovery of two new elements, cesium and rubidium, which had been detected by spectroscopy. Everything in his home laboratory was examined through the spectroscope, including the selenium wastes from 1850, which he supposed might show the spectrum of tellurium as an impurity. However, on 5 March 1861 he found an anomalous bright green line in the wastes; and by 30 March he was confident enough to announce the existence of a new element, thallium. He exhibited minute samples of thallium, in the form of a black powder, and of its salts at the International Exhibition in London in 1862, only to find that the element had been isolated simultaneously on a larger, more obviously metallic scale by the French chemist C. A. Lamy. An acrimonious controversy developed, not least because, through an administrative blunder, at first only Lamy received the exhibition’s medal. Chemical News gave Crookes prestige, but thallium (which he subsequently showed to be a widely distributed element easily extracted from the flue dust of various industrial processes) brought him fame and led to his election to the Royal Society in 1863.

From 1861 to 1871 Crookes patiently developed techniques to determine the atomic weight of thallium, deliberately modeling his standards on the hitherto exacting determinations of atomic weights that had been made by J. S. Stas. Once he had decided to make the determination by the formation of thallium nitrate from the heavy metal, and to check by the precipitation of barium sulfate from thallium sulfate, he took extraordinary pains to purify his reagents, to calibrate his platinum balance weights relative to one another, and to use an extremely sensitive Oertling balance mounted in an iron case that could be exhausted of air. Weighings could then be made at reduced pressures and reduced to a vacuum standard, thus eliminating a major source of previous analytical error, the neglect of barometric variation in gravimetry.6 The result was an atomic weight for thallium of 203.642 (that of oxygen is 15.960; the difference from the modern value, 204.39, is not a reflection on Crookes’s accuracy, but of his use of Stas’s inaccurate value for the ratio of nitrogen to oxygen).7 This seemed to indicate to Crookes that Stas was right to be skeptical of Prout’s hypothesis that atomic weights were integral multiples of the atomic weight of hydrogen. Nevertheless, as a spectroscopist faced with the bewildering complexity of spectra, Crookes could not avoid becoming a convinced believer in the complexity of the elements; and he frequently gave space in Chemical News to speculations concerning the unity of matter or the unity of matter or the relationships between elements (e.g., those of B. C. Brodie, Jr. and J. A. Newlands).

While working with his balance in a vacuum, Crookes noticed another “anomaly”: the equilibrium of the balance was disturbed by slight differences in temperature of his samples. In particular he noticed that warmer bodies appeared to be lighter than colder ones; and since this occurred in a strong vacuum, it could not be attributed to either the condensation of vapor on the cooler body or to air currents surrounding the hotter body. At first Crookes believed this was a signpost pointing to a link between heat and gravitation; and because of its bearing on the “psychic force” he was then also investigating, he subjected the anomaly to an intensive examination with the aid of Gimingham, whose skill at glassblowing and vacuum pump technology enabled them to develop a number of delicate and beautiful pieces of apparatus.

They found that if a large mass was brought close to a lighter one suspended in an evacuated in space, it was either attracted or repelled. By mounting two pith balls on a pivoted horizontal rod in a tube attached to a mercury pump, they were able to investigate the effect more closely. Since the attraction or repulsion was heightened by a decrease in pressure, Crookes was led to suppose in 1873 that “the movement is due to a repulsive action of radiation.” Repulsion was produced not only by heat radiation but also by light, and Crookes concluded—erroneously, as it turned out—that he had found a genuine case of “the pressure of light” postulated by the unfashionable corpuscular theory of light and by Maxwell’s as yet unaccepted electromagnetic theory. This belief led him in 1875 to devise the “light-mill,” or radiometer, which consisted of “four arms, suspended on a steel point resting in a cup, so that it is capable of revolving horizontally. To the extremity of each arm is fastened a thin disc of pith, lamp-blacked on one side, the black surfaces facing the same way. The whole is enclosed in a glass tube, which is then exhausted to the highest attainable point and hermetically sealed.” 8

The fascinating free rotation of the mill in strong light proved a financial boon to instrument makers, but the explanation of its action proved very difficult and controversial. In the furore, which was exacerbated by his psychic activities, Crookes tried, with difficulty, to maintain an empirical position in the battles between Osborne Reynolds, P. G. Tait and James Dewar, Arthur Schuster, and Johnstone Stoney, and in his personal vendetta with Carpenter. Eventually, in 1876, he accepted Stoney’s explanation in terms of the kinetic theory of gases: that the radiometer’s motion was due to the internal movements of the molecules in the residual gas. If the mean free path was small compared with the dimensions of the radiometer vessel, molecules that struck the warmer black vane and rebounded with increased velocity would hold back any slower-moving particles advancing toward the surface. Hence a relatively larger number of molecules would hit the cooler surface and prevent any rotation of the vanes. When the pressure was lowered, and the mean free path was large, there was no compensation of the recoil effect, and rotation took place9. This theory gave a good qualitative explanation of all Crookes’s subsequent radiometer work, although quantitative agreement was the achievement of more mathematically gifted physicists.10 Even so, in a tedious and exacting series of measurements made between 1877 and 1881, Crookes showed how the radiometer confirmed Maxwell’s prediction that the viscosity of a gas was independent of its pressure except at the highest exhaustions11.

In 1878 Crookes began a new series of research papers with the conviction “that this dark space coating [the cathode in low-pressure electrical discharges] was in some way related to the layer of molecular pressure causing movement in the radiometer”12. By attempting to determine the actual paths of “lines of molecular pressure” on the analogy of Faraday’s lines of magnetic force, Crookes came to work on the cathode rays, which until then had been the exclusive province of German experimentalists. An electric radiometer whose vanes acted as a cathode showed that the dark space separating the cathode from the cathode glow extended farther from the blackened side of the vane, and that only when the pressure was reduced to a point at which the dark space touched the sides of the radiometer tube did rotation occur. This suggested that the electric discharge in an evacuated tube (a “Crookes tube”) was an actual illumination of the lines of molecular pressure. Since the thickness of the dark space (soon called the “Crookes dark space”) increased with decrease in pressure, the kinetic theory explanation of the radiometer’s action suggested that the dark space was a measure of the length of the mean free path.

In. November 1876, Crookes introduced into his work on the molecular physics of high vacua Faraday’s beautiful concept of a fourth state of matter, “radiant matter”13. Lines of molecular pressure were now interpreted as streams of radiant matter in a highly tenuous condition; collisions between molecules were so rare that the familiar physical properties of the gaseous state of matter were modified.

With his thorough grounding in the experimentally difficult art of vacumm physics, Crookes laid the foundation for the fuller investigation by J. J. Thomson of the behavior of radiant matter in the discharge tube, showing, for example, that it induced phosphorescence in minerals like the diamond; that it caused the glass of the discharge tube to phosphoresce; that its stream could be deflected by a magnet; and, most important of all, that since it cast a shadow of an opaque object (for example, a Maltese cross), it traveled in straight lines and was corpuscular in nature 14. In 1879 he declared:

In studying this Fourth state of Matter we seem at length to have within our grasp and obedient to our control the little indivisible particles which with good warrant are supposed to constitute the physical basis of the Universe…. We have actually touched the border land where Matter and Force seem to merge into one another, the shadowy realm between Known and Unknown which for me has always had peculiar temptations. I venture to think that the greatest scientific problems of the future will find their solution in this Border Land, and even beyond; here…lie Ultimate Realities, subtle, far-reaching, wonderful.15

This may seem prescient of the electron, as radiant matter turned out to be; but for Crookes cathode rays were negatively charged molecules, and the above passage is more a hint of the occult. Until Thomson’s demonstration of the electron in 1897, Crookes’s theory of a fourth state of matter was severely criticized by the German school of physicists, who looked for an etherial wave explanation of cathode rays.

During the 1880’s Crookes followed two major research programs: the first, the technology of electric lighting with evacuated tubes, was motivated by the prospect of financial rewards; the second, the examination of the phosphorescent spectra produced by bombarding minerals with radiant matter, led him to speculate about the origin of the elements. Most substances gave continuous phosphorescent spectra, but the beautiful discontinuous spectra produced by rate earth minerals led him to suspect in 1881 that these ores contained many unknown elements. He based this belief principally on the fact that the patterns of discontinuity in the spectra could be enhanced and carried over from one manipulation to another during chemical fractionation. For example, he found that yttria could be separated by fractionation into five or more parts that were differentiated only by their slightly different solubilities in ammonia and by the different prominent lines in their phosphorescent spectra. It turned out later that Crookes had been totally misled by impurities (phosphorogens) in his samples, for, as Lecoq de Boisbaudran, Urbain, and others showed, phosphorescent spectra could be altered simply by adding traces of other earths; and ultrapurified earths were not sensibly phosphorescent. The method, therefore, turned out to be useless for characterizing elements, either known or unknown.

Nevertheless, with the aid of Gardiner, Crookes brilliantly pursued a laborious course of chemical fractionations “repeated day by day, month after month, on long rows of Winchester bottles.” Between 1886 and 1890 he concluded erroneously that yttrium, gadolinium, and samarium were complex mixtures of unknown elements; that didymium was more complex than Welsbach’s (correct) separation into neodymium and praseodymium in 1885 implied; and that erbia probably contained four elements. In 1898 he announced that an element, which he called monium or Victorium (in fact a mixture of gadolinium and terbium), could be separated from yttria. Chemists experienced great difficulty in sorting out the relationships between the rare earth elements; Crooke’s elegant researches confused matters for a number of years, for he persisted in these increasingly isolated views as late as 1906. Ironically, had he pursued the fractionation of calcium salts, which he began, he undoubtedly would have separated calcium isotopes.16

It has happened repeatedly in the history of chemistry that when the number of elements has been experimentally increased, there has been a simultaneous move to decrease their number by the introduction of a simplifying theory of matter. For Crookes, as he explained in superlative addresses to the British Association for the Advancement of Science in 1886 and to the Chemical Society in 1888, the similarity between the rare earth elements was certain evidence that they originated from a common matter.17 The idea of the chemical element, Crookes felt, had to be expanded to take into account the acceptance of the periodic law of the elements and the speculations of B. C. Brodie, T. S. Hunt, J. N. Lockyer, and others. Crookes rekindled Prout’s hypothesis by suggesting that elements were complex bodies that had developed by an inorganic process of Darwinian evolution. Before evolution had commenced, there existed a primary matter that, in an incorrect transcription from the Greek he called “protyle.” Prout had originally suggested that hydrogen might be the protyle from which other elements had formed, but sixty years of atomic weight determinations had ruled out this possibility. It was still possible to propose something with less weight than hydrogen; perhaps it was helium, the element then known to exist only in the sun.

With remarkable vision Crookes showed how the elements, with their periodic properties, could be conceived of as arising under the action of an imaginary cosmic pendulum swung by the efforts of two forces, electricity and heat (loss of temperature with time), and dampened according to the laws x = a sin(mt) (an oscillation: a and m are constants, x is the electrical force, and t is the time) and y = bt (a simple uniform motion at right angles to the oscillation: y is temperature and b is a constant). This effectively produced the curve of the periodic system that had been developed for teaching purposes by J. Emerson Reynolds.18 But genesis occurred in space. If a third oscillatory motion was conceived, z = csin (2mt) (an oscillation twice as rapid as the first and at right angles to the two former motions: c is a constant and z is an unspecified force thet is probably of electrical origin), then an actual three-dimensional figure-eight model of the genesis of the elements were located in a vertical plane on identical parts of the helix.

Crookes held no brief for Kelvin’s pessimistic “heat-death” future of the universe; on the contrary, borrowing from Stoney, he believed that the universe was in continual creation. The radiant heat from ponderable elementary matters in the center of the universe flowed toward the periphery, where it was transformed into protyle and genesis recommenced. Definite quantities of electricity were given to each element at its genesis; this electricity determined the element’s valence and, hence, its chemical properties. Atomic weight, on the other hand, was only a measure of the cooling conditions that had prevailed at the moment of the element’s birth and not, as Mendeleev had implied, a measure of its properties. If the cooling conditions had sometimes been irregular:

… elements would originate even more closely related than are nickel and cobalt, and thus we should have formed the nearly allied elements of the cerium, yttrium, and similar groups; in fact the minerals of the class of samarskite and gadolinite may be regarded as the cosmical lumber-room where the elements in a state of arrested development—the unconnected missing-links of inorganic Darwinism—are finally aggregated.19

In this way it was conceivable that the atomic weights determined by chemists really represented an average weight of several slightly different atoms.

When we say the atomic weight of, for instance, calcium is 40, we really express the fact that, while the majority of calcium atoms have an actual weight of 40, there are not a few which are represented by 39 or 41, a less number by 38 or 42, and so on.20

This explained not only why atomic weights were so persistently and tantalizingly close to integral or half-integral values but also why there was a “close mutual similarity, verging almost into identity” in the rare earth elements. Crookes called there closely related atoms “meta-elements” or “elementoids,” and in 1915 he claimed that the concept of isotopes was a vindication of his speculation. However, Crookes’s sensational concept was too closely bound up with his imaginative notion of the genesis of the elements and his misinterpreted experiments with the rare earths to be anything more than an inkling of Soddy’s isotopes, which were a solution to a different problem upon which it had no influence: that of radioactive series. In 1902 he identified protyle with the electron, and in 1908 he developed a scheme whereby many elements of high atomic weight were degraded into lower elements.

The theory of genesis was the high-water mark of Crookes’s speculative genius, and it would be difficult to find its equal in scientific literature. Even the idea of the noble gases was implicit in the double helix model he built; inevitably, in 1898, he took pains to show how well Ramsay’s and Rayleigh’s new gases fitted into his system.21In 1895 Ramsay had asked Crookes to examine the spectrum of a strange gas extracted from cleveite (uraninite), and in a famous telegram Crookes had announced it was helium.

As a product of the Royal College of Chemistry, which originally had been endowed by agricultural interests, Crookes always maintained a lively interest in agricultural matters. He translated several Continental manuals on fertilizers, and he was a powerful advocate of the use of disinfectants such as phenol in the cattle plague that swept Great Britain from 1865 to 1867. As president of the British Association in 1898 he used his platform not only to summarize his interests in science and the occult but also to warn the world that it would be faced by starvation, because of the failure of wheat supplies to keep abreast of population, unless science found new sources of fertilizers. Many took this as sensationalism, but Crookes had intended to be optimistic that chemists could and would solve the problem of tapping the huge supplies of atmospheric nitrogen for fertilizers. His sensible remarks on the wheat problem caused a furore among economists and politicians and were a factor in the motives that drove O. C. Birkeland and Fritz Haber to develop industrial processes for nitrogen fixation.

In 1900 Crookes was sixty-eight; yet far from retiring from research, he threw himself wholeheartedly into solving the new conundrum of radioactivity, driven in part by the knowledge that a sojourn in South Africa in 1895 had prevented him from beating Roentgen to the discovery of X rays. Despite his speculative powers, Crookes at first took a conservative view of this new science, for he could not believe that radioactive elements decayed spontaneously, since this seemed to imply a violation of the conservation of energy. It was his view, expressed between 1898 and 1900, that the source of activity was external to the radioactive element. He imagined that radium, say, had the ability to act as a Maxwellian demon and select from the atmosphere those air particles which were moving more swiftly than the average, absorb some of their energy, and eject them at a lower speed.

This theory, which never received full publication, contravened the second law of thermodynamics; and although Crookes thought that he might have experimental support for it, his evidence did not measure up to the critical scrutiny of Stokes.22 In December 1900 he confided to Stokes that he believed radio-activity was due to “bodies smaller than atoms,” and by 1906 he had fully accepted Rutherford’s subatomic transmutation theory of radioactivity. Crookes had supplied a fundamental datum for this theory in 1900, when, using photographic plates as indicators of activity, he had shown that if uranium was purified, it could be separated chemically into a nonactive portion and a radioactive portion that he called uranium X. In 1901 Becquerel showed that within a few months the uranium X had lost much of its activity, whereas the previously inactive portion of the separated uranium had regained its radioactivity and would produce further quantities of uranium X. Soddy subsequently showed that Crookes’s use of photographic plates masked the fact that uranium emitted α rays, whereas uranium X emitted penetrating β rays. As if in answer to this, in 1903 Crookes developed the spinthariscope, a device whereby the α particles emitted from a sample of a radioactive material were indirectly rendered visible through a simple microscope by their bombardment of a phosphorescent zinc sulfide screen.23 Even after the invention of more sophisticated electric counting devices, Rutherford and his co-workers used this scintillation-counting method for the estimation of α activity.

Although Crookes produced a dozen more experimental papers between 1910 and 1919, his ability to keep abreast, and ahead, of his contemporaries inevitably declined. His presidency of the Royal Society from 1913 to 1915 was marred not only by the outbreak of war but also by a degree of ill feeling from the younger generation of fellows that he had sowed the wild oats of genius past his allotted time.


1. “The Preparation of Eye-preserving Glass for Spectacles,” in Philosophical Transactions of the Royal Society, 214A (1914), 1–25.

2. W. B. Carpenter, “The Radiometer and Its Lessons,” in Nineteenth Century, 1 (1877), 242–256.

3. “On the Supposed ‘New Force’ of M. J. Thore,” in Philosophical Transactions of the Royal Society, 178A (1888), 451–469.

4. E. E. F. d’Albe, Life of Crookes, pp. 404–406.

5. Speech at banquet for past presidents of the Chemical Society, in Chemical News, 102 (1910), 252.

6. “Researches on the Atomic Weight of Thallium,” in Philosophical Transactions of the Royal Society, 163 (1875), 277–330. In modern gravimetry reduction of weighings to a vacuum standard is made from calibration tables, and it is not necessary to use a vacuum balance except in the most rigorous investigations.

7. All Stas’s weighings were based on a silver standard of 107.93 (modern, 107.880). This gave an atomic weight of nitrogen of 14.04 (modern, 14.008) and helped to lower Crookes’s value for thallium, estimated from thallium nitrate, by 0.1 percent. The atomic weight of silver was reappraised by Alexander Scott and Theodore Richards between 1900 and 1910.

8. “On the Attraction and Repulsion Resulting From Radiation,” in Proceedings of the Royal Society, 23 (1874–1875), 373–378.

9. “On Repulsion Resulting From Radiation, Parts III and IV,” in Philosophical Transactions of the Royal Society, 166 (1877), 325–376; see 375–376, added 17 January 1877.

10. In fact the simple kinetic theory explanation later rejected by Maxwell and Reynolds. Unequal heating of the radiometer vanes led to a temperature gradient that caused “thermal creep” or vortex motions of the gas particles. A rise in pressure occurred on the hotter side of the vanes, which consequently moved away from the incident radiation. See J. Clerk Maxwell, “On Stresses in Rarified Gases Arising From Inequalities of Temperature,” ibid., 170 (1879), 231–256; and O. Reynolds, “On Certain Dimensional Properties of Gases,” ibid., 727–845.

11. “On the Viscosity of Gases at High Temperatures,” ibid., 172 (1881), 387–434.

12. “On the Illumination of Lines of Molecular Pressure, and the Trajectory of Molecules,” ibid., 170 (1879), 135–164; quotation, 135.

13. “Experimental Contributions to the Theory of the Radiometer,” in Proceedings of the Royal Society, 25 (1876–1877), 304–314; see 308.

14. See also C. F. Varley, “Some Experiments on the Discharge of Electricity Through Rarified Media and the Atmosphere,” ibid., 19 (1870–1871), 236–240.

15. “Radiant Matter,”in Chemical News, 40 (1879), 91–93, 104–107, 127–131; see 130–131.

16. Crookes, “On the Fractionation of Yttria,” ibid., 54 (1886), 158.

17.Reports of the British Association for the Advancement of Science, 55 (1886), 558–576; Journal of the Chemical Society, 53 (1888), 487–504.

18. J. E. Reynolds, “Note on a Method of Illustrating the Periodic Law,” in Chemical New, 54 (1886), 1–4.

19.Reports of the British Association for the Advancement of Science, 55 (1886), 558–576; see 569.


21. “On the position of Helium, Argon, and Krypton in the Scheme of Elements,” in Proceedings of the Royal Society, 63 (1898), 408–411.

22. “Sur la source de l’energic dans les corps radio-actifs,” in Compte rendu hebdomadaire de I’Academie des sciences, 128 (1899), 176–178; Larmor, Stokes Correspondence, I , 487–481; see also J. Elster and H. Geitel, “Versuche an Becquerelstrahlen,” in Annalen der physik, 66 (1898), 735–740.

23. “Certain Properties of the Emanations of Radium,” in Chemical News,87 (1903), 241.


I Original Works. Crookes published between 250 and 300papers, many of which are scattered through obscure Victorian newspapers and periodicals. A fairly complete list of his papers may be composed from Royal Society Catalogue of Scientific Papers (1800–1900); Index to the Proceedings of the Royal Society of London (Old Series) vols.1–75, 1800–1905 (London, 1913); and Index to the Proceedings of the Royal Society of London (1905–1930) and to the Philosophical Transactions of the Royal Society of London (1901–1930) (London, 1932). Articles in Nature and Popular Science Review may be traced by consulting the not entirely reliable indexes of these journals. A large number of uncataloged papers will be found in the defunct journals that Crookes edited during the years noted: Liverpool Photographic Journal (1857–1858), Photographic News (1858–1859), Chemical News (1859–1919; from 1906 until its failure in October 1932, this was edited by Crookes’s assistant, J. H. Gardiner), Quarterly Journal of Science (1864–1878), Journal of Science (1879–1885), Electrical News and Telegraphic Reporter (1875). In addition the following are important articles: T. Belt (Crooker’s patent agent), “Improvements in Gold and Silver Amalgamation,” in Mining Journal, 35 (1865), 407; “Another Lesson From the Radiometer,” in Nineteenth Century, 1 (1877), 879–887; and “Some Possibilities of Electricity,” in Fortnightly Review, 51 (1892), 173–181.

Crookes’s writins on the paranormal that were not republished in his book of 1874 include “On the Scientific Investigation of Psychic Phenomena,” in The Spiritualist (15 June 1871), 161; “A Scientific Examination of Mrs. Fay’s Mediumship,” ibid. (12 Mar. 1875), 126–128; his dispute with J. Spiller over Home’s mediumship, in The Echo (Nov. 1871), passim, and in English Mechanic and World of Science, 14 (1871), 200, 253, 327; his dispute with W. B. Carpenter over Mrs. Fay, in Nature, 17 (1877), 7–8, 43–44, 200; “Notes on Seances With D. D. Home,” in Proceedings of the Society for Psychical Research, 6 (1889–1890), 98–127; “Differences in ‘Psychical Phenomena’ With Eusapia Paladino and D. D. Home,” in journal of the Society for Psychical Research, 6 (1893–1894), 341–345; “Experiments With D. D. Home,” ibid., 9 (1899–1900), 147–148, 324; “Presidential Address,” in Presidential Addresses to the Society for Psychical Research, 1882–1911 (London, 1912), pp. 86–103. These psychic writings, as well as other unpublished letters, are to be published by R. G. Medhurst and Mrs.K. M. Goldney.

Crookes published the following books: A Handbook to the Waxed Paper Process in Photography (London, 1857); On the Application of Disinfectants in Arresting the Spread of the Cattle Plague (London, 1866), offprinted from Third Report of the Commissioners Appointed to Inquire Into the Origin of the Cattle Plague; On the Manufacture of Beet-Root Sugar in England and Ireland (London, 1870); Select Methods in Chemical Analysis (Chiefly Inorganic) (London, 1871; 2nd ed., 1886; 3rd ed., 1894; 4th ed., 1905); Researches in the Phenomena of Spiritualism (London, 1874; reissued London, 1903, 1953; Manchester, 1926), also in several translations; A Practical Handbook of Dyeing and Calico Printing (London, 1874 ; 2nd ed., 1883); Dyeing and Tissue Printing (London, 1882); London Water Supply (London, 1882), a report presented to the Local Government Board by Crookes, W. Olding, and C. Meymott Tidy; The Wheat Problem (London, 1899; 2nd ed., 1905; 3rd ed., 1917); and Diamonds (London, 1909).

Crooks also translated and edited B. Kerl, A Practical Treatise on Metallurgy (London, 1868), adapted with the help of E. Rohrig; M. Reimann, On Aniline and Its Derivates (London, 1868); R. Wagner, A Handbook of Chemical Technology (London, 1872) and Manual of Chemical Technology (London, 1892); G. Auerbach, Anthracen (London, 1877); G. Ville, On Artificial Manures (London, 1879 2nd ed., 1882; 3rd ed., 1909) and The Perplexed Farmer (London, 1891); and K. B. Lehmann, Methods of Practical Hygiene, 2 vols. (London, 1893).

Crookes edited M. Faraday, A Course of Six Lectures on the Various Forces of Matter and Their Relations to Each Other (London, 1860; many reprints) and Chemical History of A Candle (London, 1861; many reprints); W. Odling, A Courses of Six Lectures on the Chemical Changes of Carbon (London, 1869); and J. Mitchell, A Manual of Practical Assaying (3rd ed., London, 1868; 4th ed., 1873; 5th ed., 1881; 6th ed., 1888). Patent literature should be consulted for Crookes’s several specifications.

Crooke’s unpublished material was extensive. E. E. F. d’Albe (below) had some 40,000 documents available to him in 1923. Most of these have disappeared; but some have been dispersed to Science Museum Library, London: laboratory weighing book, 1860–1862; laboratory notebooks, vols. 1–5, 1876–1881, mainly in the hand of Gimingham; and 51 letters from Crookes to Gimingham (1871–1877); Science Museum, London: notebook containing newspaper clippings on thallium, 1861–1864; Royal Institution, London : laboratory notebooks, vols. 6–21, 1881–1919, mainly in the hand of Gardiner; Royal Society, London; correspondence with J. F. W. Herschel, Arthur Schuster, and others; Imperial College archives, London: correspondence with Henry E. Armstrong and S. P. Thompson; University College, London: Sir William Ramsay archive; Wellcome Historical Medical Library, London: correspondence with John Spiller; Psychical Research Society, London: miscellaneous correspondence and Sir Oliver Lodge papers; Cambridge University library: papers of Sir George Stokes; and Britten Memorial Library, The Spiritualists’ National Union, Ltd., Tib Lane, Manchester: uncataloged miscellaneous correspondence.

Examples of Crookes’s radiometers, discharge tubes, and other apparatus may be seen at the Royal Institution and the Science Museum, London, where a mercury pump by Gimingham should also be studied. Crookes’s personal effects may be appraised from John Butler and Co., Ltd., Auction Sale of Sir William Crookes (London, n.d.), the sole copy of which is in the Oxford Museum of the History of Science, Gabb papers, item 7.

II. Secondary Lieterature. In view of the wholesale destruction of manuscripts after 1923 the fundamental source is E. E. Fournier d’Albe, The Life of Sir William Crookes O. M., F. R. S. (London, 1923); see informative reviews by Sir Oliver Lodge, in Proceedings of the Society for Psychical Research, 34 (1924), 310–323, with a “correction” in the Journal of the Society for Psychical Research, 22 (1925–1926), 80; and by A. Smithells, in Nature, 113 (1924), 227–228. For a complete list of the honors awarded to Crookes, see Who was Who, II (4th ed., London, 1967), 247–248. Obituaries and articles that add significantly to d’Able are (listed chronologically) P. Zeeman, “Scientific Worthies: Sir William Crookes, F. R. S.,” in Nature, 77 (1907–1908), 1–3;A. Tilden, obituary, in Proceedings of the Royal Society, 96A (1920), i-ix, reprinted with additions in his Famous Chemists (London, 1921), pp. 259–272; Sir W. Barrett, obituary, in Proceedings of the Society for PsysicalResearch, 31 (1921), 12–29; K. Przibram, “Crookes,” in G. Bugge, ed., Das Buch der grossen Chemiker (Leipzig, 1930), II, 288–297; Lord Rayleigh, “Some Reminiscences of Scientific Workers of the Past Generation and Their Surroundings,” in Proceedings of the Physical Society, 48 (1936), 236–242, with photographs of Crookes’s laboratories; O. T. Rotini, “Una lettera inedita di J. S. Stas [to Crookes] sopra l’ipotesi di Prout,” in Actes du VIIIe Congres international d’histiore des sciences (Florence-Milan, 1956) (Paris, 1958), II, 486–496; F. Greenaway, “A Victorian Scientist: The Experimental Researches of Sir William Crookes (1832–1919),” in Proceedings of the Royal Institution of Great Britain, 39 (1962), 172–198; A. E. Woodruff, “William Crookes and the Radiometer,” in Isis, 57 (1966), 188–198; and J. C. Chaston, “Sir William Crookes, Investigations on Indium Crucibles and the Volatility of the Platinum Metals,” in Platinum Metals Review, 13 (1969), 68–72.

For Crookes’s work with disinfectants, see S. A. Hall, “The Cattle plague of 1865,” in Medical History, 6 (1962), 45–58. A useful survey of the context of Crookes’s work on rare earths is J. W. Mellor, A Comprehensive Treatise on Inorganic and Theoretical Chemistry, 16 vols. (London, 1922–1937), V, 497–503. His work on helium is discussed in M. W. Travers, A Life of Sir William Ramsay, K. C. B., F. R. S. (London, 1956), Passim (index unreliable). On the cooperation with Stokes, consult J. Larmor, ed., Memoir and Scientific Correspondence of the Late Sir George Gabriel Stokes, Bart., 2 vols. (Cambridge, 1907), esp. II. 362–494.

The violent controversies over Crookes’s interest in the paranormal are best explored through a critical appraisal of T. H. Hall, The spiritualists, the Story of Florence Cook and William Crookes (London, 1962); R. G. Medhurst and K. M. Goldney, “William Crookes and the Physical Phenomena of Mediumship,” in Proceedings of the Society for Psychical Research, 54 (1963–1966), 25–157; E. J. Dingwall, The Critics’ Dilemma (Crowhurst, Sussex, 1966); and A. Gauld, Founders of Psychical Research (London, 1968).

W. H. Brock