4:58 Scientific Intelligence. 



a current of water to circulate from the upper end of tbe tube 

 to the lower. The great heat, however, was excited in the capil- 

 lary of the tube. Quartz prepared by the method of Professor 

 Shenstone possesses the property of resisting changes of tem- 

 perature in a remarkable manner. One of these quartz tubes can 

 be heated to a white heat and plunged into water without crack- 

 ing. 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 window, 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 poten- 

 tial of twenty thousand volts, condenser -3 microfarads, an 

 extremelj^ 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 strait 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 b}'' 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 

 another instance of selective solarization mentioned in my pre- 

 vious paper. The strongest metallic lines or gaseous lines are not 

 those which show the strongest reversal. For instance, the cal- 

 cium line at approximately 4227 is strongly reversed, while the 

 stronger 3968, 3933 do not show a reversal, except with much 

 stronger and longer continued discharges. 



A careful inspection of the negatives shows that the reversals 

 of the metallic lines occur when the}^ fall on bright gaseous 

 lines or bands. In the same way a bright gaseous line falling on 

 a continuous spectrum can show a similar reversal. We can 

 express this in symbolic language as follows : let A represent the 

 intensity of the line and B the amount of the previous action of 

 light on the photographic plate, then the reversal appears to be 

 proportional to AB. 



It seems probable that there are similar reversed lines running 

 through the solar spectrum and I hope to detect them. 



This investigation shows that the presence of dark lines in the 

 spectra of stars does not imply necessarily the presence of revers- 

 ing layers of a colder state of the gases; for such reversal may 

 arise from photographic action on the plates which are used. 

 Moreover a gas may show a continuous spectrum to the eye, or 

 even when photography is employed with glass tubes and glass 

 lenses ; while with quartz tubes such as I have employed a large 



