4'30 



NATURE 



[December i6, 19 15 



ing. out three tons of this intermediate product 

 daily, A remarkable and novel development has 

 arisen in this branch of the colour industry. The 

 firms engaged in dyeing aniline black are setting 

 up small aniline plants costing 300L to 400I. 

 each, capable, under the supervision of one opera- 

 tive, of producing daily 100 lb. of aniline from 

 benzene. 



At present the seven companies engaged on 

 finished coal-tar dyes are restricting drastically 

 the number of colours produced, and are concen- 

 trating on increased output. Two works are 

 specialising in an ample supply of chlorodinitro- 

 benzene, from which two other well-equipped 

 factories are manufacturing sulphide black on a 

 huge scale. Synthetic indigo is receiving the 

 attention of four powerful chemical companies. 



Although the existing equipment for natural 

 dyes installed in six large American works has 

 proved to be a national asset of great value, yet 

 the total supply of dyes is still far short of 

 customary requirements, and the American public 

 is urged to meet the abnormal situation in a 

 spirit of generous compromise. The existing 

 shortage will soon disappear, inasmuch as the 

 United States possess all the enterprise, inventive 

 talent, and technical ability requisite for the de- 

 velopment of an American dye industry. As re- 

 gards the practical experience of industrial colour 

 syntheses, it is suggested that the services of a 

 corps of expert Swiss colour chemists would be 

 of untold value in accelerating the evolution of 

 the new industry. This scheme has already been 

 adopted successfully in Russia, where a group of 

 dye consumers have formed a company, including 

 as a constituent member a leading Basle firm, 

 which supplies a technical staff to the enterprise. 



One reason for the former dominance of German 

 colour chemistry was the unity and solidarity of 

 the various firms engaged in this industry, so that 

 when one was menaced by any foreign competitor 

 they all acted in unison. In America the field 

 has been entered by many separated interests im- 

 perfectly acquainted with the complexity of the 

 colour problem. A plea for a higher degree of 

 unity is put forward in order to avoid overlapping 

 and duplication of effort. It has been pro- 

 posed to establish Government factories for the 

 production of coal-tar intermediates, these fac- 

 tories to be available for manufacturing explosives 

 in case of war. A national bureau of standards 

 for dyestufifs would afford considerable protection 

 to the growing industry, and a similar result 

 would be attained by organising the consumers 

 of dyes. 



In view of these developments, it appears cer- 

 tain that in a few years America will be practically 

 self-contained as regards dyes. It is not at all 

 probable that the vast industrial organisations by 

 this time established will content themselves with 

 catering only for the American market, especially 

 as the United States possess sufficient of the 

 needed raw materials to supply the whole world's 

 dye industry. British dye producers must expect 

 to face, not only furtive attempts to recover trade 

 NO. 2407, VOL. 96] 



by German competitors, but also a direct frontal 

 attack on their home, colonial, and foreign 

 markets by dye-wares of American origin. The 

 only way of meeting this invasion will be by a 

 combination, first of British manufacturers among 

 themselves, and secondly a co-operative union of 

 the British group with similar groups represent- 

 ing the other nations of the Quadruple Entente. 

 The pooling of our resources for war will need 

 to be followed by a partnership in original ideas, 

 technical organisation, and natural resources in 

 regard to the chemical industries of the allied 

 nations. G. T. M. 



OPTICAL INVESTIGATION OF ETHER- 

 DRIFT. 



OF all the attempts made to detect a possible 

 influence of the motion of the medium on 

 optical phenomena, the only one giving a positive 

 result, was the celebrated experiment of Fizeau, 

 in which interference was produced between two 

 beams of light which passed along tubes con- 

 taining running water, the one beam going with 

 the current and the other beam against it. When 

 the direction of the current was reversed the 

 bands were displaced, and the displacement could 

 be explained on the assumption that the ether in 

 the tubes drifted with the current with a velocity 

 v(i — i/fi^), where v is the velocity of the water. 

 Fizeau obtained a 14 per cent, agreement between 

 theory and experiment, which was regarded as 

 satisfactory in view of the difficulty of the subject. 

 The experiment was afterwards repeated by 

 Michelson and Morley with more refined means, 

 and they obtained a difference of less than i per 

 cent, with a calculated probable error of about 

 5 per cent. 



In 1895, however, in his " Versuch einer Theorie 

 der electrischen und optischen Erscheinungen in 

 bewegten Korpern," Lorentz gave a new expres- 

 sion for the velocity of the ether drift, namely : — 





This expression is also obtained on the theory of 

 relativity. In the case of water it is quite 3 per 

 cent, larger than Fresnel's value. We have just 

 received two papers reprinted from the Proceed- 

 ings of the Amsterdam Academy, which describe 

 an elaborate experimental investigation made by 

 Prof. Zeeman at Amsterdam to decide between 

 the two expressions. (Vol. xvii., pp. 445-451, 

 1914, and vol. xviii., pp. 398-408, 1915.) 



The interference fringes were produced by 

 Michelson 's method. The length of the tubes was 

 6 metres and the maximum velocity of the water 

 5-5 metres per second. As the expression to be 

 tested varies only slightly with the wave-length, 

 the light of an arc lamp could be used as source 

 after it passed through a monochromator. The 

 fringes were recorded photographically ; the 

 cross-wires in the focal plane of the telescope 

 came out on the negative, and the displacement 

 of the fringes relative to the cross-wires was 



