686 PROCEEDINGS OF THE AMERICAN ACADEMY. 



although the intensity of the lines coinciding with the H.H. lines, if they 

 were calcium lines, would require the presence of these lines. 



A series of experiments was undertaken with metallic terminals one 

 centimeter apart, in lead glass. The diameter of the capillary varied 

 from one to two millimeters. A spectrum similar to that of Figure 4 was 

 obtained with the addition of certain lead lines, several of which were 

 reversed on the side toward the ultra violet. The portion of these lines 

 not reversed broadened toward the red end of the spectrum ; and this 

 broadening increased with the intensity of the discharge (Figure 7). 

 No calcium lines appeared. When cadmium terminals were used many 

 of the cadmium lines were reversed, and here also the bright portion of 

 these lines was much broadened. In the case of cadmium no other 

 lines was observed (Figure 6). The gaseous ions contributed little or 

 nothing to the photographic effect. 



When iron terminals were employed no iron lines were obtained even 

 when the terminals were only three millimeters apart; nevertheless the 

 lines and bands usually attributed to silicon came out with great in- 

 tensity. When, however, aluminum terminals were substituted for iron 

 terminals, aluminum lines, together with the supposititious silicon lines, 

 were obtained. It was noticeable that the two lines coinciding with 

 H.H. lines of the solar spectrum did not appear, while the two charac- 

 teristic aluminum lines between the H.H lines came out reversed. The 

 lines corresponding with the H.H. lines always appeared when a dis- 

 charge of like intensity produced the spectrum of aluminum in air. 



The iron of which the terminals were made was ordinary soft iron, 

 with a melting point not far from 1100°, while the melting point of 

 aluminum is between 700° and 800°. If the silicon is volatilized it is 

 difficult to see why the iron gave no spectrum, while the aluminum 

 yielded one, for there is not a very great difference between their melt- 

 ing points. 



Another series of experiments then were made with metallic terminals 

 in quartz capillaries varying in internal diameter from two to three 

 millimeters, the terminals being one centimeter apart. The same spectra 

 were observed as are represented in Figure 3, with an absence of the 

 lines corresponding with the solar H.H. lines. This absence was no- 

 ticeable, also, when metallic terminals were one centimeter apart in lead 

 glass. Iron terminals gave no iron lines in the quartz tubes, while alu- 

 minum lines appeared when aluminum terminals were used instead of 

 iron terminals. 



When the metallic terminals were placed three millimeters apart in 



