154 Prof. Trowbridge on the Spectra of Hydrogen. 



in quartz, I had the ends of the tubes ground smooth, and 

 the glass-blower of the laboratory prepared glass bnlbs in 

 which suitable electrodes were inserted. These bulbs were 

 luted to the ends of the quartz tubes. In certain cases metal 

 plates were luted directly to the ends of the quartz tubes. I 

 employed silicate of soda as a luting agent ; and after this 

 had hardened I applied on the outside of the joint a hard 

 preparation of pitch and shellac. 



The glass bulbs were covered with other bulbs which 

 allowed a current of water to circulate from the upper end 

 of the tube to the lower ; great heat, however, was ex- 

 cited in the capillary of the tube. Quartz prepared by the 

 method of Professor Shenstone possesses the property of 

 resisting changes of temperature in a remarkable manner. 

 One of these quartz tubes can be heated to a white heat and 

 plunged into water without cracking. Such tubes, therefore, 

 are very valuable for the experiments I have been conducting 

 on gases at high temperature. 



They also possess the great advantage over end-on tubes of 

 glass provided with quartz windows, that the capillary can be 

 placed close to the slit of the spectroscope, thus giving a 

 very intense light and a broad spectrum ; moreover, the 

 quartz is not melted by the intense heat. A photograph of 

 gaseous spectra can be obtained with a single discharge and 

 a very narrow slit ; with tubes filled with hydrogen excited 

 by a difference of potential of twenty thousand volts, con- 

 denser '3 microfarads, an extremely intense light is obtained. 

 This light is dazzling white with a bluish cast : it has more 

 than three times the actinic effect of the same quantity of 

 electricity discharged between magnesium terminals. Viewed 

 with a straight-vision spectroscope the spectrum appears 

 continuous; and even photography fails to reveal bright 

 lines between the HH lines and the red end of the spectrum. 

 In the region, however, beyond the limit set by the absorption 

 of the glass Geissler tubes there are both bright lines and 

 dark lines. The principal reversed lines are at wave-lengths — 



2889-70 



2549-89 



2528-60 



2524-29 



2519-3 



2516-21 



These lines correspond with the lines of silicon volatilized 

 by the spark in air. It seems that we have in this phenomenon 



