Chemistry and Physics. 75 



is not insignificant. Mr. Moll studied the cause of these varia- 

 tions, and repeated the work of Nyland, Mayer and Holtz with 

 arrangements similar to those used by these investigators. It 

 proved in all these experiments that the nature of the discharge 

 was a little altered by the mode of observation itself, since in the 

 experiments of Nyland and Mayer the spark struck through a 

 sheet of paper, and in those of Holtz the spark itself was in rota- 

 tion. From these defects the arrangement of Rood is free. 



If it is desired to give an explanation of the discharge of a 

 Ruhnikorff inductorium, it is necessary at the outset to decide 

 whether the partial sparks are directed in the same way or not. 

 Mr. Moll allowed the sparks to fall on a rotating disc of paper, 

 the electrodes on either side of the paper being at slightly differ- 

 ent distances from the center of the disc. The holes made by the 

 sparks were always opposite one of these electrodes, consequently 

 all the sparks have the same direction. 



Starting from this fact the author endeavors to explain the 

 phenomena of the discharge by the assumption that the electricity 

 cannot flow with sufficient rapidity to the electrodes, and that 

 partial sparks are produced as soon as the difference of potential 

 has reached a certain value, dependent on the distance of the 

 electrodes apart, etc. The approximative statements which with 

 the help of known facts one can easily deduce from these condi- 

 tions, agree, as a whole, very well with the results previously 

 found by experiment. — k. a. 



8. Photography in Colors. — The Comptes Rendus for Feb- 

 ruary, 1891, contained a note on color photography describing a 

 method employed by M. G. Lippmann, who had been able to pro- 

 duce photographically the image of the spectrum with all its 

 colors. M. G. Lipmann has communicated further results to the 

 Comptes Rendus for April 25 (No. 17, vol. cxiv). The following 

 is a translation of his last communication: — In the first communi- 

 cation which I had the honor to make to the Academy on this 

 subject, I stated that the sensitive films that I then employed 

 failed in sensitiveness and isochromatism, and that these defects 

 were the chief obstacle to the general application of the method 

 that I suggested. Since then I have succeeded in improving the 

 sensitive film, and, although much still remains to be done, the 

 new results are sufficiently encouraging to permit me to place 

 them before the Academy. 



On the albumen-bromide of silver films, rendered orthochromatic 

 by azalin and cyanin, I have obtained very brilliant photographs 

 of spectra. All the colors appear at once, even the red, without 

 the interposition of colored screens, and after an exposure varying 

 from five to thirty seconds. On two of these cliches it has been 

 remarked that the colors seen by transmission are very plainly 

 complementary to those that are seen by reflection. The theory 

 shows that the complex colors that adorn natural objects ought 

 to be photographed just the same as the simple colors of a spec- 

 trum. The four cliches that I have the honor of submitting to 



