228 PROCEEDINGS OF THE AMERICAN ACADEMY 



XVI. 



CONTRIBUTIONS FROM THE PHYSICAL LABORATORY OF 

 HARVARD COLLEGE. 



No. IX. — CONDENSERS AND GEISSLER'S TUBES. 

 Br William P. Wilson. 



In the secondary circuit of a RulimkorfF's coil of 6000 ohms resist- 

 ance was joined a galvanometer, and successively Geissler's tubes con- 

 taining GO, H, and 0. The galvanometer was constructed from a 

 Rdhmkorff's coil equal in resistance to the one used in the secondary 

 circuit. Upon sending a spark through a Geissler's tube of GO, a 

 deflection of 8 centimetres was given by the galvanometer. 



The light was strongest in the centre of the tube ; near the positive 

 and negative poles of the platinum electrodes it was very feeble. 



The color in the middle of the tube shaded into red ; at the ex- 

 tremities it was a pale bluish-white. The light in the enlarged part 

 of the tube, approaching the positive pole, was beautifully stratified 

 with alternate light and dark bands. A condenser, consisting of a 

 Leyden jar of 60.5 sq. cm. surface, was connected with the opposite 

 poles of the coil, and a spark again passed through the Geissler's tube. 

 The galvanometer gave the same deflection of 8 cm. as before, but the 

 difference in light was very marked. This increase in light did not 

 show itself in the centre of the tube, but towards the extremities ; both 

 poles, and especially the positive, becoming much more brilliant. The 

 dark and light bands seen near the positive pole, before the introduc- 

 tion of the condenser, now entix-ely disappeared. The Geissler's tube 

 was removed, and an equal air resistance substituted. This was done 

 by placing near together, and in line, the broken ends of the wire. 

 By a micrometer adjustment, these wire points could be made to recede 

 from or approach eacii other, until the galvanometer gave a deflection 

 of 8 cm. with the condenser in the circuit. Upon sending a spark 

 through this air resistance, having previously disconnected the con- 

 denser, the deflection of the galvanometer was at once increased from 

 8 to 20 cm. The light did not vary as much as in the Geissler's tube, 



