228 PROCEEDINGS OF THE AMERICAN ACADEMY 



XVI. 



COXTRIBUTIOXS FROM THE PHYSICAL LABORATORY OF 



HARVARD COLLEGE. 



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

 By William P. Wilson. 



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

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

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

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

 circuit. U23on sending a spark through a Geissler's tube of CO, 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 66.5 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 entirely 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 each 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 26 cm. The light did not vary as much as in the Geissler's tube, 



