July 20, 1900.] 



SCIENCE. 



107 



the Joint Transmission of Direct and Alter- 

 nating Currents. ' The author showed that 

 when direct and alternating currents are 

 sent over the same line, each behaves as if 

 the other were not there, and that thus the 

 same line can be used for two separate sys- 

 tems of transmission of energy, at the cost 

 of a single line. This would seem to remove 

 the last objection to the general use of the 

 alternating current system and it is probable 

 that the method will be extensively used. 



In a paper on the ' Visible Radiation 

 from Carbon,' Professor Mchols brought 

 out the surprising fact that the radiation 

 from carbons of the types used in incan- 

 descent lamp filaments is not, as has hitherto 

 been generally assumed, of the same type 

 as that from a perfectly black body, but 

 that the radiation is selective, the radiation 

 from that part of the spectrum between the 

 red or the yellow being much greater than 

 it is in the case of a black body. It thus 

 becomes impossible to estimate the temper- 

 ature of heated carbon from its radiation, 

 but on the other hand a number of ques- 

 tions of the greatest interest are opened up 

 which we may hope Professor ISTichols' 

 further researches will explain and which 

 will result in considerable extensions to 

 our knowledge of the subject. 



In a paper by Professors Guthe and 

 Trowbridge on the ' Coherer,' the, authors 

 find that their experiments on the properties 

 of contacts can all be expressed by a single 

 differential equation. A large number of 

 facts are thus simply correlated, and a 

 striking advance made in the theory of the 

 subject. 



Of a paper by Frank Allen on the ' Effect 

 upon the Persistence of Vision of Exposing 

 the Eye to Light of Various Wave Lengths,' 

 in which a method suggested by Professor 

 Nichols was used, it can only be said that 

 it is one of those papers in regard to which, 

 notwithstanding the apparent absence of all 

 flaws in the admirable expeiimental work 



we are forced to reserve our opinion, since 

 the results obtained are so utterly at vari- 

 ance with our preconceived ideas. No 

 one, for example, who has done much 

 spectro-photometry, would have anticipated 

 that it would have been possible to obtain 

 color curves of subjects on different days 

 to an accuracy of less than two per cent. 

 Again, the fact, brought out by the author's 

 work, that an eye fatigued by yellow has its 

 persistence altered for the red and green 

 and not for the yellow which originally 

 fatigued it, is apparently inconceivable. 



But it is one of the fine things of science 

 that it is perpetually impressing upon us 

 the fact that we do not know everything 

 yet, even in those cases where we are apt to 

 feel that we can be most positive, so that 

 the truly scientific man must be, at the 

 same time very conservative, and yet capa- 

 ble of even greater efforts of mental gym- 

 nastics than Alice's White Queen, whom 

 conscientious practice, in conjunction with 

 shutting the eyes and breathing hard, had 

 enabled to believe no less than six impossi- 

 ble things before breakfast. And it is quite 

 possible that further evidence will show 

 that we must really change our precon- 

 ceived ideas in regard to color in a number 

 of important respects. Accepting the ex- 

 perimental results, there would seem, as the 

 author pointed out, no escape from the con- 

 clusion that the three fundamental color 

 sensations are those of the red, green and 

 violet. This is a most important result, 

 and is to a certain extent corroborated by 

 Mr. Ives, who in the course of a charming 

 exposition of his thi-ee color processes during 

 the meeting, took occasion to point out that 

 the only screens which gave satisfactory re- 

 sults for such work were a red, a green and 

 a blue-violet one. 



Another very valuable paper was that by 

 Merritt, on ' The Production of Kathode 

 Rays by Ultra- Violet Light.' A charged 

 disc was illuminated by ultra-violet light, 



