382 PROCEEDINGS OF THE AMERICAN ACADEMY 



the current passes, it ts accompanied hy stratification, — in other words, 

 by a molecular vibration, or the formation of waves rapidly propagated 

 through the gas or vapor, — and that the increasing rarefaction allows a 

 greater amplitude for the oscillations, and thus gives rise to longer and 

 longer waves ? 



In referring to the actinism of the electric light, Professor Rogers 

 described some experiments which, with the aid of Mr. Ritchie and 

 the distinguished photograper, Mr. Black, he had lately made on the 

 photographic energy of the different colored lights of the Geissler 

 vacuum-tubes. These, he stated, were but preliminary to more ex- 

 tensive observations on the subject, which he hoped, through the same 

 kind aid, to be able to report on hereafter. The most striking results 

 thus far noted are the following : — 



1. The faint, bluish light surrounding the negative wire is superior 

 in actinic power to the more brilliant glow of the opposite bulb of the 

 apparatus. 



2. The actinism of the rays emerging from the tube is greatly in- 

 creased by passing them through a solution of sulphate of quinine, so 

 as to impress them with the Jluorescent character. 



3. The time required for a distinct photographic impression was 

 greatly less than by the ordinary daylight. In the case of a narrow 

 tube transmitting a bright purplish flash, a strong picture was made on 

 the collodion plate in less than half a second. This corresponded to 

 one turn of the ratchet-wheel, or twelve successive flashes of light 

 passed through the tube. Allowing each flash to occupy tenfold the 

 time of an electric spark, as measured by Wheatstone, we should have 

 an aggregate of time during which the twelve flashes acted of less than 

 TonWxrth of a second. 



A number of positive impressions on paper, printed from 

 the original collodion surfaces, were exhibited as results of 

 these preliminary experiments. 



On motion of Dr. C. T. Jackson, the thanks of the Acad- 

 emy were voted to Mr. Ritchie for his interesting and brilliant 

 exhibition. 



