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Rh be a better term. The three-sensation theory is only one explanation of the fact that when spectra! green and spectral red are mixed they make yellow. The explanation that when red and green are mixed the resulting impulses cannot be distinguished by the nerve cells from those caused by simple yellow is sufficient. This explana- tion is supported by the fact that the trichromic see yellow as red- green. There is no evidence that the assumptions of the three-sensa- tion theory are true. Simple yellow cannot be. split up into its hypothetical red and green constituents. An hour's dark adapta- tion does not alter the hue of spectral yellow. As blue is supposed to be made up chiefly of the green and violet sensations, and yellow to be made up chiefly of red and green sensations, the green element should be affected after fatigue with blue, and yellow viewed sub- sequently should appear red. This is not the case. The eye may also be fatigued with spectral yellow, so that all yellow disappears from the spectrum without affecting the appearance of a very feeble red. It is known that if the intensity of a number of coloured lights be reduced in the same proportion all the colours do not disappear at the same moment. If, therefore, spectral yellow were a compound sensation it should change colour on being reduced in intensity. If, however, spectral yellow be isolated in the spectrometer, and the intensity be gradually reduced by moving the source of light away, the yellow becomes whiter and whiter until it becomes colourless, but does not change in hue.

In cases where a subjective red is seen with an illumination by white light, this red is seen with a compound yellow but not with a simple spectral yellow.

When the theory is applied to colour-blindness it is still more unsatisfactory and is quite unable to explain the fundamental facts, as for instance why the colour-blind should make an increased mono- chromatic division in the spectrum or why certain colour-blind per- sons should be able to pass the wool test. Again no explanation is offered of the fact that simultaneous contrast is increased in the colour-blind. One of the best-known cases of colour-blindness, a simple dichromic, was classified by one expert as a case of complete red-blindness and by another as a case of complete green-blindness! The present writer has never examined a single case of colour- blindness which, on a detailed examination with spectral colours, could be explained on the three-sensation theory. For instance, a case of shortening of the red end of the spectrum may be taken in which the red is shortened to X68o; at X6/o the perception of red may be defective to about half the normal and at X66o it may be quite normal. This can be proved with a colour-mixing apparatus with the equation X67O+535 =Xy8<). If red X66o be substituted for red X6?o an absolutely nor nal match will be made ; if red of X6/O be used, twice as much red will be put in the mixed colour as with the normal, and if red of X68o be used a match is quite impossible in any circumstances. Now on the three-sensation theory a case of this kind may be classed as -5 red-blind, all the ordinates of his red sensation curve being supposed to be reduced to one-half of the normal, but the red in the shortened portion should according to this hypothesis be brought up to the normal by doubling the amount of red, whereas it will be found when there is complete shortening that any amount of red light f ro n the shortened portion may be added without being perceived. In another way it can be conclusively proved that the shortening is not produced by the diminution of a hypothetical red sensation which is stimulated by rays from every part of the spectrum. A man with shortening of the red end of the spectrum wilt match as identical pink and blue wools, the pink wool appearing much lighter to the normal-sighted than the blue one. If these two wools be now viewed through a blue-green glass which is opaque to the rays occupying the shortened portion, they will appear identical in hue and shade. It should be noted that whilst the blue-green glass cuts off the physical red rays it transmits numerous rays supposed to stimulate the red sensation.

When three selected spectral colours, for instance red, green and violet, are mixed in suitable proportions a white is made which will exactly match the white fro n which the spectrum was formed. On the three-sensation theory the two are physiologically identical, that is to say, the three hypothetical sensations are stimulated in similar proportions by the mixture and by the white light, though the two are physically different. It is essential to the three-sensation theory that after fatig-le (say) to red or green the match should still remain, and supporters of the theory state that no change is observed in these circumstances. This, however, is not the case, and if a number of normal-sighted persons view the white equation after fatigue with red light, which is supposed to affect only the hypo- thetical red sensation, the match is no longer correct, and a very remarkable fact becomes apparent, namely, that much more red will be required in the mixed white.

The mixed white appears a bright green to a person whose eyes have been fatigued for red, and in order to make a match the amount of green has to be reduced to about one-half, so that the mixture now appears bright red to a normal-sighted person with unfatigued eyes.

See F. W. Edridge-Green, The Physiology of Vision (G. Bell & Sons, London, 1920). (F. W. E.-G.) COLUMBIA UNIVERSITY (see 6.739). The work of Columbia University during the period 1910-20 was greatly extended. A school of journalism was founded in 1912, a school of business in 1915, and a school of dentistry in 1917. In order to render the largest possible service to the community, courses in university extension were organized for men and women who could give only a portion of their time to study, but who desired to pursue subjects included in a liberal education. These courses, as such, did not lead to degrees, but might be offered as credit toward a degree under one of the faculties. Under university extension there was organized also an institute of arts and sciences which conducted series of lectures and recitals of a popular nature, as well as a system of courses for home study for persons unable to attend classes in the university. These courses also did not lead to academic credit or degrees. In 1920 there were in Columbia University in all departments 1,150 instructors and administrative officers, and in the twelve months ending June 30 1920, 28,314 students were enrolled. Of these, roughly one- third were registered in the 1919 summer session; one-third in the degree-granting schools and faculties during the academic year 1919-20; and one-third in university extension during the academic year 1919-20.

The productive endowment of the university, including the endowments of Teachers College, Barnard College, and the College of Pharmacy, amounted in 1920 to $47,000,000, which, added to the property occupied for educational purposes, made a total capital investment of $72,000,000. To meet the increased costs of education, the fees in the several schools were raised so that they ranged in 1921 from $250 to $350. The alumni of the university were given a definite part in the government of the institution by an agreement under which six of the 24 trustees were elected on alumni nomination. In 1912 the corporate title of the university was changed from the

Trustees of Columbia College in the City of New York " to the " Trustees of Columbia University in the City of New York."

The university took an active part in the World War. Immedi- ately upon the severance of diplomatic relations with Germany in Feb. 1917, it placed its resources, both physical and intellectual, at the service of the Government. There were established at the university schools for training men for both the army and the navy, including work in radio, photography, quartermaster's routine, explosives, gas engines, submarine detection, and the Student Army training corps, which prepared men for the various officers' training camps of both armed services. Students, faculty and alumni to the number of 4.125 were enlisted in the army and navy, and 2,175 left their previous occupations and assisted the Government in some one of the civilian branches. Two hundred Columbia men died in the war. (N. M. B.)

COLVIN, SIR SIDNEY (1845- ), English man of letters (see 6.748), was knighted in 1911, and retired from his position in the British Museum in 1912. In 1911 he published an edition of the Letters of R. L. Stevenson and in 1917 John Keats, His Life and Poetry. His autobiographical Memoirs and Places appeared in Nov. 1921.

COMBES, [JUSTIN LOUIS] ÉMILE (1835-1921), French statesman (see 6.751). The campaign for the separation of Church and State was the last big political action in his life. While still possessed of great influence over extreme Radicals, M. Combes took but little public part in politics after his resignation of the premiership in 1905. He joined the Briand Ministry of Oct. 1915 as one of the five Elder Statesmen, but without portfolio. He died May 26 1921.

COMMERCE, DEPARTMENT OF, one of the executive departments of the U. S. Government. It succeeded the earlier Department of Commerce and Labor, by an Act of Congress, approved March 4 1913, which also created a separate and independent Department of Labor (see LABOR, DEPARTMENT OF). The Secretary of Commerce is a member of the president's Cabinet but is not in line of succession to the presidency. It is his duty to promote the commerce, domestic and foreign, of the United States. There is also an assistant secretary and a solicitor, the latter acting as legal adviser to the Secretary and to the heads of the various bureaus of the department.

As originally organized there were 9 bureaus, as follows: (i) The bureau of the census, charged with the collection of data concerning population, agriculture, manufactures, mining, etc. ; (2) the bureau of foreign and domestic commerce, for the collection and diffusion of information of use to the manufacturer and exporter; (3) the coast