192 



BARUS— ADJUSTMENT FOR PLANE GRATING. [April 24, 



The change of voltage throughout the main contours of the curves 

 is almost a linear variation with the lapse of time, except that at the 

 beginning the motion is accelerated from rest as usual ; for instance : 



Time 



Va 



•3 1-5 



12 

 3-7 



16 

 6.1 



24 



II.O 



28 

 134 



32 

 15-5 



60 sec. 

 31.0 cm. 



cJ^^g 2 



OJCCf 3Z 



qe 1Z0 



C/i&C. 



4. Aluminum Tube Charged zvith Radium Tubelets I.-V.: Data. 

 — The air in the condenser C is now highly ionized and its voltage 

 becomes appreciable. The data obtained are given in Fig. 2. The 

 needle is positively charged, thus impelling positive charge toward 

 the quadrants. In the four series of data observed the aluminum 

 core of the condenser is twice joined to the electrometer, the 

 brass shell being put to earth (series i and 4) and twice com- 

 mutated (aluminum to earth series 2 and 3). The results are 

 identical except that in series 3 the insulation was perhaps better, or 

 Va may have changed. The accelerated march of the needle from 

 rest is obvious in both curves and is thus independent of the sign of 

 the limiting voltage, V . It may be mere inertia, but it is of less 

 consequence here because the initial data are not needed in the 

 following computation. 



