358 



Dr. Carl Barus on the Efficiency of 



the measurable coronas as far as the large green -blue-purple 

 or the bluish type, the largest of the useful coronas producible 

 in a fog-chamber by any means whatever. Moreover, it is 

 merely necessary to open the stop-cock as rapidly as possible 

 by hand, using easily devised annular oil- troughs at top and 

 bottom of the plug, both to eliminate all possible ingress of 

 room-air and to reduce friction. Fog-chambers larger than 

 the one measured were often used, and it is curious to note 

 that the efficiency of such chambers breaks down at a certain 

 high exhaustion abruptly, while up to this point (varjang^ 

 greatly from chamber to chamber) different apparatus behave 

 nearly alike. The vacuum-chamber is put in connexion with 

 an air-pump, the fog-chamber with a. well-packed filter by 

 the aid of stop-cocks. Water nuclei are precipitated between 

 exhaustions from the partially exhausted fog-chamber. 



2. The Variables. — After reading the initial pressures of 

 the fog- and vacuum-chambers, it is expedient to open the 

 stop-cock quickly and thereafter to close it at once before 

 proceeding to the measurement of the coronas. Eventually, 

 i. <?. when the temperature is the same in both the fog- and 

 vacuum-chambers, they must again be put in communication 

 and the pressures noted, if the details of the experiment are 

 to be computed. 



The following series of variables (Table I.), where p denotes 

 pressure, p density, t absolute temperature, it vapour pres- 

 sure, is to be considered. The ratio of volumes of the fog- 

 and vacuum-chambers was v/V = *064. 



Table I. — Notation. 

 Drop of pressure 8p=p— p s , observed: Bp~p^-p 2 , computed. 



States 

 No. 



Fog-Chamber. 



Yacuum-Chamber. 



Remarks. 



1 



P 



' 



r 



TT 



P' 



P 



1 



T 1 



7T 



Initial states. Chambers 

 separated. 



2 



'Pi 



Px 



T i 



""l 



1\ 



Pi 



r l 



«■/ 



Adiabatie states, after ex- 

 haustion. Chambers com- 

 muuicating. 



3 



¥i 



Pi 



^ 



7T, 



Pi 



Pi' 



1 



*l 



Do., after condensation of 

 water in the fog-chamber. 



4 



P* 



P 2 



T 



7T 



P-2 



P-2 



T 



TV 



Chambers separated before 

 condensation ensued. Ori- 

 ginal temperature regained. 



5 



p* 



Pa 



r 



7T 



V4 



N 



' 



77 



Chambers separated after 

 condensation. Original tem- 

 perature regained. 



6 



ih 



P 3 



T 



7T 



Pi 



Pi 



T 



7T 



Chambers communicating 

 after exhaustion. Original 

 temperature restored. 



