Brown, Alexander Crum

(b. Edinburgh, Scotland, 26 March 1838; d. Edinburgh, 28 October 1922)

Chemistry, Physiology.

Crum Brown was the son of Rev. John Brown, a Secessionist minister, and Margaret Crum. His uncle, Walter Crum, was a chemist and fellow of the Royal Society. He went to Mill Hill School, London, and then Edinburgh University, where he studied medicine. He graduated in 1858, and in 1861 he received the M.D. for a thesis on the theory of chemical combination. In 1862 Crum Brown was awarded a D.Sc. by London University. In the same year, he went to Germany, where he worked under Kolbe and carried out what was probably the first synthesis of adipic acid. Returning to Edinburgh in 1863, he was appointed lecturer in chemistry, and professor in 1869, a position he held until 1908. He became a fellow of the Royal Society in 1879, and from 1891 to 1893 was president of the Chemical Society.

In his thesis Crum Brown discussed chemical structure and the application of mathematics to chemistry, the subjects that interested him most. The first attempts had just been made to represent the structure of compounds by various types of graphical formulas. Crum Brown was dissatisfied with the unwieldy diagrams invented by Kekulé and proposed a more convenient scheme. He represented constituent atoms by circles drawn around the usual letter symbols, with a number of lines proceeding from them according to their valences. He indicated atomic linkage by lines, first dotted and later solid. In 1865 he invented the symbol, which is still in use, of two parallel lines for a double bond. Unknown to him, Archibald Couper, also in Edinburgh, had already employed a similar system of letters and lines. However, the graphical formulas used today most resemble those suggested by Crum Brown. The latter were popularized by Frankland, who adopted them throughout his lectures.

Also in structural chemistry, in 1892 Crum Brown put forward the rule determining the positions of groups entering the benzene ring in the substitution of monoderivatives.

He was convinced that chemistry would one day achieve the perfection of a mathematical science. This was a common feeling, earlier expressed by Davy and Herschel. Crum Brown was inspired by a belief in the unified plan of the Creation. This would be revealed in the ultimate reduction of all physical sciences to dynamics. Just as optics and heat, in their maturity, had become branches of applied mathematics, so he expected chemistry, undeveloped and fragmentary, eventually to be mathematically deducible from mechanics. In 1867 he showed how some steps might be taken in this direction. Regarding chemical substances as operands and the processes performed on them as operators, he derived mathematical expressions corresponding to successive chemical substitutions. Although it was similar in appearance to Brodie’s more elaborate operational calculus, his work was distinct from this. He thought Brodie had been “too severe” on chemists who had used atomic language, and insisted that it could be adopted without believing in atoms. He stated that while physics showed matter to be molecular, chemists could use atomic symbols without concern for their physical significance. Even if matter were proved to be continuous, his graphical formulas would still be useful. This common pragmatic attitude to the atomic theory was soon attacked by Williamson. Crum Brown’s address to the British Association in 1874 was a more realistic approach. Neither he nor Brodie made any lasting contribution to mathematical chemistry.

In physiology Crum Brown was fascinated by the effects produced through rotation. He investigated the various sensations of vertigo in a subject rotating blindfolded on a table. He correctly related these to the motion of liquid in the semicircular canals of the inner ear. His work appeared soon after Mach and Breuer had given the same explanation, but his theory was an advance in that it detailed the coordinated action of the canals on both sides of the head, which Mach had rejected. Crum Brown stated for the first time that the two horizontal canals differed from one another in that they received their stimuli from motions in opposite directions, thus allowing a blindfolded subject to distinguish between rotations to the left and to the right. To illustrate his theory, he constructed a mechanical model. This consisted of two heavy wheels fixed horizontally and side by side so that they could rotate about a vertical axis in opposite directions. Each wheel had a stop that prevented its rotation beyond a certain point in one direction; its rotation in the opposite direction was restricted by the stretching of a spring. The axle of each wheel contained an adjustable stopcock, which widened as the springs stretched and through which gas was passed from pipes and ignited.

Crum Brown said that the wheels represented the horizontal canals of the ear and that the inertia of the former corresponded with the inertia of the fluid contained in the latter. The stretching of the springs represented the stretching of the ampullae. The variation in the flames that occurred as the springs stretched and relaxed during the rotation of the wheels illustrated the different brain messages transmitted by the nerves as their endings were stimulated by the stretching of the ampullae during the rotation of the body.

BIBLIOGRAPHY

Crum Brown’s papers are listed in the Royal Society Catalogue of Scientific Papers, I (1867); V (1877); IX (1891); XIII (1914). His other publications are in the British MuseumGeneral Catalogue of Printed Books, XXVII (1965). Ernst Mach discussed Crum Brown’s work on rotation in his Grundlinien der Lehre von den Bewegungsempfindungen (Leipzig, 1875), pp. 104–110. Some useful information can be found in the obituary notice “Alexander Crum Brown,” in Journal of the Chemical Society, 123 (1923), 3422–3431. See also David F. Larder, “Alexander Crum Brown and his Doctoral Thesis of 1861,” in Ambix, 14 (1967), 112–132.

D. C. Goodman