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Lockyer, Joseph Norman

Lockyer, Joseph Norman

(b. Rugby, England, 17 May 1836; d. Salcombe Regis, England, 16 August 1920)

astrophysics.

Lockyer came from a middle-class family, derived, it was believed, from early Celtic immigrants from France into England. His father, Joseph Hooley Lockyer, was a surgeon-apothecary with broad scientific interests, and his mother, Anne Norman, was a daughter of Edward Norman, the squire of Cosford, Warwickshire. His formal education, at schools in the English Midlands, tended to concentrate on the classics, but the scientific atmosphere at home, supplemented by travel in Switzerland and France, served to broaden his interests and to produce the type of mind that was later to show a marked versatility. His earliest employment was as a civil servant in the English War Office, which he entered in 1857. He remained there until his striking success as an amateur astronomer led, via a period of temporary service as secretary of the duke of Devonshire’s commission on scientific instruction, to a permanent post under the Science and Art Department, which culminated in his appointment as director of the Solar Physics Observatory established at South Kensington. There he remained until, in 1911, the observatory was transferred, much to his disappointment, to Cambridge, whereupon he retired.

In 1858 he married Winifred James, who died in 1879, leaving seven children, and in 1903 he married Thomasine Mary, the younger daughter of S. Woolcott Browne and widow of Bernhard E. Brodhurst, F.R.C.S., who survived him. After leaving the Solar Physics Observatory he established an observatory near his home in Salcombe Regis, Devonshire, known at first as the Hill Observatory and after his death as the Norman Lockyer Observatory—an institution now attached to the University of Exeter. Lockyer’s interests, though very wide, were dominated by his belief in science and its potentialities for the welfare of the human race. Nevertheless, he published, with the collaboration of his daughter Winifred, Tennyson as a Student and a Poet of Nature—inspired by his friendship with the poet. He took more than a nominal interest in his membership of the Anglican Church, while on the lighter side he was stimulated to write The Rules of Golf: He received numerous honors from scientific bodies throughout the course of a long and exceptionally active life.

The direction of Lockyer’s early scientific investigations was determined by the fact that the spectroscope was just beginning to reveal its great possibilities as an almost miraculous means of probing the secrets of nature. It was in 1859 that Kirchhoff and Bunsen laid the foundations of astrophysics by showing how the composition of the heavenly bodies could be determined—a problem not long before selected by Auguste Comte as a type of the permanently insoluble. Lockyer, thrilled by the new prospect thus opened up, obtained a spectroscope, which he attached to his 6¼-inch refracting telescope, and began a series of observations which, in 1868, brought him his first major success—the observation, at times other than during a total solar eclipse, of the solar prominences. The dramatic circumstances attending this discovery doubtless added to the attention which it received, but the ingenuity of the method and the importance of its implications would alone have entitled it to full credit.

The observation depended on the possibility of using a dispersion large enough to weaken the spectrum of the diffused sunlight in the atmosphere sufficiently to make visible the bright lines of the prominence spectrum. Lockyer conceived the idea as early as 1866, but, through a series of delays in obtaining a satisfactory instrument, it was not until 20 October 1868 that he was able to observe the prominence spectrum. It happened that on 18 August 1868 a total eclipse of the sun was visible in India, at which the brilliance of the prominence spectrum lines suggested to Jules Janssen, who observed them, the same idea that had occurred long before to Lockyer; and on the following day he successfully applied it. Both Lockyer and Janssen transmitted the news of the discovery to a meeting of the French Academy of Sciences, and by a remarkable coincidence the messages were received within a few minutes of one another. The French government commemorated the event by striking a medal bearing the portraits of the two astronomers.

Following up the observations, Lockyer soon observed a yellow line in the prominence spectrum, and in that of the outer atmosphere of the sun (which he similarly discovered and named the “chromosphere”), which had not been produced in the laboratory. This suggested to him the existence in the sun of an unknown element, which he named helium. In this he ran counter to the general opinion, which was that the line was due to a familiar element under exceptional conditions of excitation; and it was not until 1895 that William Ramsay, by producing the line from terrestrial sources, verified Lockyer’s early conclusion. The constitution of the sun remained a leading interest with Lockyer, and he conducted many solar eclipse expeditions with a view to establishing ideas which he had formed from his studies of laboratory spectra.

One of the most conspicuous of such ideas was the “dissociation hypothesis,” which much later acquired a special significance through developments in the theory of spectra. Lockyer observed in his experiments that the spectrum of an element varied with the intensity of the stimulus used to produce it. This appeared incompatible with the general view that the spectrum of any element was an invariable characteristic of the atoms (or molecules) of the element itself. It was recognized that the spectra of atoms and of molecules, even of the same element, differed; and Lockyer, following this clue, postulated that a stimulus greater than that necessary to break up the molecule into atoms would break up the atoms themselves and produce subatoms having their own characteristic spectra. The observation that, as he believed, the spectra of different elements contained lines in common led to the hypothesis that the atoms of what were known to the chemist as elements were themselves groupings of smaller constituents, the common lines being due to such constituents obtained by the dissociation of atoms of different elements.

This idea, like many of Lockyer’s speculations, met with almost universal opposition, but although, in its original form, it is now believed to be groundless, it is recognized that it contains more than a germ of truth. It is now held that an increase in the energy of stimulus does indeed produce a dissociation of the atoms, and that atoms of different elements are indeed composed of different associations of the same more elementary components; but the apparent coincidences of lines from different elements are found, with the greater accuracy of measurement now possible, to be illusory. Although each element can yield a succession of spectra (silicon, for instance, to take one of Lockyer’s own examples, under continuously increasing stimulus yields spectra known as Si I, Si II, Si III, Si IV), these are all different from any other spectrum that can be produced from anything at all. The data accumulated by Lockyer and, under his direction, by his students and assistants proved of the greatest value when a more tenable explanation became possible.

Another idea of Lockyer’s connected with his observations of the sun, to which he devoted much attention and which likewise has not—at least in its original form—been strongly substantiated, was the supposed connection between the sunspot cycle and terrestrial meteorology. The eleven-year cycle of sunspots has been correlated, with greater or less plausibility, with various terrestrial phenomena, but what was peculiar to Lockyer’s view of the matter was that he attempted to connect it with his idea of dissociation. He observed that certain lines in the spectra of sunspots varied in width during the course of a cycle, and this to him denoted a change of physical conditions in the sun that manifested itself in parallel effects in the spectra of the spots and in the weather on the earth. These phenomena were thus related not as cause to effect but as effects of the same cause which he postulated as pulsations in the sun. This work came to an abrupt end with the transfer of the Solar Physics Observatory to Cambridge and has not had any significant development.

Perhaps the most far-reaching of Lockyer’s ideas was his meteoritic hypothesis, which is one of the most comprehensive schemes of inorganic evolution ever devised and which, though almost none of it now survives, led him to conceptions far in advance of those prevalent in his day. It may be summed up in his own words: “All self-luminous bodies in the celestial spaces are composed either of swarms of meteorites or of masses of meteoritic vapour produced by heat.” The idea arose gradually in his mind from a variety of circumstances, but the crucial evidence, as he believed, lay in the examination of the spectra of meteorites under varying conditions. He believed that, by enclosing meteorites in vacuum tubes and subjecting them to gradually increasing degrees of temperature and electrical excitation, he could retrace the course of celestial evolution, and his endeavors for many years were concentrated on the establishment of a parallelism between the various types of meteoritic spectra and the spectra of the several kinds of heavenly body.

Lockyer had the good fortune to witness the very striking meteoric display of 1866, which appears to have left an indelible impression on his mind and predisposed him to give special attention to meteorites when later he began to speculate on the possibility of determining the course of celestial evolution in the light of spectroscopic evidence. Observations of Coggia’s comet, which appeared in 1874, produced a further impulse in this direction—a close association between comets and meteors was already known—and he naturally associated the successive changes in the spectrum of the comet with the changes of laboratory spectra that had created in his mind the idea of dissociation. The ultimate result was an all-comprehensive scheme of the following character.

In the beginning space was occupied by a more or less uniform distribution of meteorites which, through their rapid motions and chance collisions, tended to accumulate in groups. These developed in various ways according to the conditions, giving rise to the various types of heavenly body observed. Very large loose groups would constitute nebulae, within which further condensations would occur, destined to become stars. A star, beginning as a meteoritic swarm, would rise in temperature as it condensed, until a stage was reached at which the mass, then completely vaporized, would lose heat by radiation at a rate equal to its generation by condensation; thereafter it would cool down toward its final state as a cold solid body. An exceptionally rapid conglomeration would constitute a nova, or new star, of which Lockyer examined some specimens that appeared during his working life; it would rise rapidly to its maximum temperature, and then decline in the normal stellar manner. Original groupings too small to become nebulae would form comets, while a number of isolated meteors would remain to enter the earth’s atmosphere and appear as meteor swarms and occasionally as a meteorite large enough to reach the earth’s surface. The final state of the universe would be that of a number of cold, dark bodies moving about aimlessly forever.

The correlation of the various types of celestial spectra with the succession of meteoritic spectra observed in the laboratory was carried out by Lockyer with great ingenuity but, it must be admitted, with insufficient critical power and too great a tendency to special pleading. A band spectrum arising from molecules presents the appearance, under small dispersion, of bright strips, each sharp at one edge and gradually fading out at the other, until, after a short dark gap, the sharp edge of the next appears. Now it is possible to regard this, in spectra so imperfect as those then obtainable from faint celestial sources, in the opposite way—as a dark band with a sharp edge, gradually growing into brightness in the reverse direction and ending abruptly at the beginning of the next dark band. In that case it would be an absorption instead of an emission spectrum, the substances present revealing themselves by the absorption of light from a strip of continuous radiation produced by a remoter source, and the identification of the substances would accordingly be quite different from that which the assumption of an emission spectrum would yield. Lockyer felt himself free to adopt either explanation, and to allow liberally for errors of measurement, according to the needs of his hypothesis, and it is not surprising that the conclusions he reached failed to convince the more critical of his contemporaries.

One of the most striking features of the hypothesis, however, that aroused some of the strongest opposition, was its implication that a star began as a cold body, rose to a maximum temperature, and then cooled down again, so that the coolest stars observable belonged to two groups, young and old. It was generally held that stars were born hot and cooled continuously throughout their lives, and the succession of stellar spectra was held to support this. According to Lockyer’s idea, however, spectra of very young and very old stars, though very similar because their temperatures, the main determining characteristic, were the same, should differ in detail because of the much greater density of the old stars compared with the young. His chief activity in astronomical research during his later years was devoted to the classification of the cooler stars according to criteria which he devised.

It is a striking fact that, before his death, the theory of stellar evolution advanced by Henry Norris Russell and widely accepted, though having no connection with the meteoritic hypothesis, required just such a life history, so far as temperature and density were concerned, as that envisaged by Lockyer; and a really satisfactory criterion was discovered—which Lockyer just missed—for distinguishing young and old (giant and dwarf, as they were called) cool stars from one another. This partial vindication of his ideas gave him great satisfaction in his closing years. The fact that the whole problem now appears much more complex than either Lockyer or Russell could have conceived does not detract from the value of their work as a stimulus to further progress.

Another activity of Lockyer’s restless mind was the astronomical interpretation of eastern temples and prehistoric stone circles, of which many examples are to be found in the British Isles. His idea was that these structures were connected with sun and star worship, their orientation being toward the points of rising or setting of conspicuous heavenly bodies. If that were so, a method existed, he conceived, of dating these erections, because our knowledge of the precession of the equinoxes enabled us to determine the precise azimuths of such risings and settings at different epochs, and if a particular temple axis pointed reasonably close to such an azimuth for a particular bright star, it could be assumed that the temple was erected when that star would be on the horizon at the point where the temple axis met it. More cautious archaeologists, while evincing considerable skepticism concerning the fundamental idea, were deterred also by the fact that the erosion of centuries, or even millennia, would have changed the visible horizon too drastically for the method to have much value; but Lockyer exhibited the same fertility of imagination in overcoming such difficulties as he had shown in connection with celestial spectra, and he built up an imposing system of dates associated with a few stars which he regarded as having had special religious significance.

Perhaps the most lasting of Lockyer’s achievements was his creation of the scientific journal Nature, which, beginning in 1869, he edited for the first fifty years of its existence. Nature is now, by common consent, the world’s leading general scientific periodical, but for many years it had to struggle to keep alive, and no small credit is due to Lockyer, and the publishers of that time, Messrs. Macmillan, whose faith in its ultimate success led them to persevere in the face of what at the earlier stages must have appeared almost insuperable obstacles. When Lockyer retired from the editorship in 1919 he was succeeded by his former assistant, Sir Richard Gregory, who held the office for the next twenty years.

This was perhaps the most outstanding example of Lockyer’s lifelong concern for the recognition of science as a most potent agent in the general progress of civilization. Of his many efforts toward this end it is impossible to omit mention of one which arose from his election as president of the British Association for the Advancement of Science in 1903. His address on “The Influence of Brain Power on History” was intended to stimulate the Association to an extension of its activities from the pursuit of pure science into the realization of another of the objects of its founders—“to obtain a more general attention to the objects of science and a removal of any disadvantages of a public kind which impede its progress.” Being unable to carry the council with him to the extent that he desired, he thereupon founded a new body, the British Science Guild, with this as its main object This organization continued to function until after his death, when the gradual recognition by the British Association that this duty indeed properly lay upon it, led to the Guild relinquishing its activities to the Association.

Lockyer is an outstanding example of the adventurous rather than the critical scientist. It is easy to find faults in his advocacy of his ideas; it is not so easy to estimate the influence of those ideas on those who were stimulated to oppose them. Just as his speculations aroused either enthusiastic support or, more often, violent dissent but never indifference, so did his person: he had devoted friends and implacable enemies. His effect on the course of science is impossible to assess, but it is undoubtedly greater than the fate of his particular speculations would suggest.

BIBLIOGRAPHY

Lockyer wrote many papers and books on astrophysics. Most of the papers were published in the Proceedings of the Royal Society or Philosophical Transactions of the Royal Society. His major books are Contributions to Solar Physics (London, 1874), containing an account of his early observations of the sun by his new method; Chemistry of the Sun (London, 1887), in which the dissociation hypothesis and the evidence for it are presented; The Meteoritic Hypothesis (London, 1890); The Dawn of Astronomy (London, 1894), explaining the method of dating ancient structures and the results of its application; and Inorganic Evolution (London, 1900), which describes the most developed form of the hypothesis and its significance for celestial spectroscopy.

The main source of information concerning Lockyer is the biography by his widow and daughter, T. Mary Lockyer and Winifred L. Lockyer: The Life and Work of Sir Norman Lockyer (London, 1928). See also A. J. Meadows, Science and Controversy: a Biography of Sir Norman Lockyer (London, 1972).

Herbert Dingle

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