388 Profs. Percy Frankland and Marshall Ward. 



Experiments with the Light of the Electric Arc, and others. 



In order to test the validity of previous conclusions as to the 

 essential similarity of action of the electric and solar light, I started 

 the following experiments. In spite of the kindness of my colleagues, 

 Professor Stocker and Mr. Shields, in lending me. the apparatus and 

 use of a dark room, and the assistance of Mr. "West, who took a 

 lot of trouble in helping me, I had to abandon these experiments, 

 partly because the lamp was not sufficiently powerful, and partly 

 owing to the close attention and long periods of watching they 

 require, and also because of other difficulties. I carried them 

 sufficiently far, however, to show that the matter is worth further 

 attention, and append the results in the hope that someone will take 

 up this line of investigation. 



On July 13 I tried the effect of exposing spores, in weak- 

 gelatine, over the water and the bichromate screens, to the electric 

 arc-light, reflected up from silvered mirrors. 



The lamp used was a small, old-fashioned Dubosq, and the micro- 

 scopes, with shades, match-box screens, quartz, and controls, &c., 

 arranged exactly as before, were 3 ft. from the arc. The current used 

 was equal to 8 amperes, and was taken from 32 storage cells. NV> 

 reflectors or lenses were used, and much light was lost. 



The spores were sown at 3 P.M., and the exposures began at 

 3.15. 



The temperatures remained the same, or varied similarly, in both 

 cultures, and during the whole period of exposure 3 hours only 

 rose from 18 C. to 19'25 C. 



On stopping the experiment at 6.15 P.M., the cultures were at once- 

 placed in the dark, side by side, at 18 C. The temperature slowly 

 fell to 16 C. at 10.45, when no results were observed. 



At 7 A.M., on the 14th July, the bichromate culture showed rodlets 

 and filaments 250 fi long and upwards ; but the culture over water did 

 not show a single germinated spore. 



I was not entirely satisfied with this result, however, because the 

 gelatine 'drop had run a little, owing to condensation of water, and 

 therefore regarded the result as negative. 



On July 14 this experiment was repeated exactly, the spores 

 being sown at 9 A.M. and exposed at 9.15 A.M. The spectra of the 

 screens were carefully examined, and everything arranged as exactly 

 as possible. 



The temperatures were as follows : 



