26S Pwpin — Action of Vacuum Discharge Streamers. 



action. The probability of the correctness of the other view 

 is therefore considerably strengthened. 



The apparatus for this experiment was constructed with two 

 other objects in view, which ought to be mentioned here. 



1st. To locate the phosphorescence. In this I was quite suc- 

 cessful. It surrounded the hottest parts of the discharge, and 

 therefore it was most intense in the narrow parts of the appa- 

 ratus. Within the reservoir it extended from c to cl in form 

 of something like an ellipsoid of revolution, with the extremi- 

 ties of its longest axis at c and d, and at times this ellipsoid 

 did not fill out the reservoir at all, which proves that the 

 phosphorescent light in this part of the apparatus is due to the 

 phosphorescence of the rarefied air and not to the phospho- 

 rescence of the glass, although in the narrower parts of the 

 apparatus where the hot discharge was very near the glass the 

 glass was also phosphorescent. 



2d. To study what I call the ramification of the discharge. 

 As soon as the pressure reached a certain limit the luminosity 

 in the bulbs (which at low pressures was more or less uniformly 

 diffused throughout the bulbs) became streaked, and at still 

 higher pressures the whole discharge in its path through the 

 bulbs divided itself into a number of distinct streamers, the 

 number of streamers diminishing with the increase of pres- 

 sure ; given pressures produced invariably the same number 

 of streamers. In this experiment I did not succeed in reduc- 

 ing the number of these streamers to less than tw T o. The 

 streamers rotated more or less uniformly in one direction or 

 the other. The angular velocity of rotation seemed to increase 

 considerably with the current of the discharge. 



An exhausted glass bulb without electrodes when brought 

 into the vicinity of these discharges emits a faint yellowish 

 light which looks very much like the light of some forms of the 

 aurora borealis. The bulb seems to remain perfectly cool. 

 Lack of time and facilities have prevented me from ■ deter- 

 mining the spectrum of this cold glow. 



My thanks are due to Professors "W. P. Trowbridge and 

 J. K. Pees for the interest which they took in my work ; also 

 to Mr. Mann, of the Astronomical Observatory, for the very 

 valuable service which he rendered to me in photographing 

 these discharges. 



1 hope to continue this work with improved facilities as soon 

 as time will permit. 



Department of Electrical Engineering, Columbia College, February 28th, 1892. 



