Gases and 3 fetal s at Hufli 'rempevatures. Gl 



all appreciable amount ot' lead in its composition. The capil- 

 lary ^vas 2 millimetres internal diameter, and 4 inches in 

 length. The pressure of hydrogen was 1 millimetre. It 

 is noticeable that the lines which coincide with the H.H lines 

 are not accompanied by the lines wave-lengths 3737 and 3706; 

 although the intensity o£ the lines coinciding with the H.H 

 lines, \i they were calcium lines, would require the presence 

 of these lines. 



A series of experiments were undertaken with metallic 

 terminals 1 centimetre apart in lead glass. The diameter 

 o£ the capillary varied from 1 to 2 millimetres. A 

 spectrum similar to that of fig. 4 was obtained with the 

 addition of certain lead lines, several of which were reversed 

 on the side towards the ultra-violet. The portion of these 

 lines not reversed broadened towards the red end of the 

 spectrum; and this broadening increased with the intensity of 

 the discharge (fig. 7). No calcium lines appeared. When 

 cadmium terminals were used many of the cadmium lines 

 were reversed ; and here also the bright portions of these lines 

 were much broadened. In the case of cadmium no other 

 lines were observed (fig. 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 3 milli- 

 metres apart ; nevertheless the lines and bands usually attri- 

 buted to silicon came out with great intensity. When, 

 however, aluminium terminals were substituted for iron termi- 

 nals, aluminium lines together with the supposititious silicon 

 lines were obtained (fig. 5). It was noticeable that the two 

 lines coinciding with H.H lines of the solar spectrum did not 

 appear, while the tw^o characteristic aluminium lines between 

 the H.H lines came out reversed. The lines corresponding 

 with the H.H lines always appeared when a discharge of 

 like intensity produced the spectrum of aluminium 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 aluminium is between 700 and 800. If the 

 silicon is volatilized, it is difficult to see why the iron gave 

 no spectrum while the aluminium yielded one ; for there is 

 not a very great difference between their melting-points. 



Another series of experiments then were made with metallic 

 terminals in quartz capillaries varying in internal diameter 

 from 2 to 3 millimetres, the terminals being 1 centimetre 

 apart. The same spectra were observed as are repre- 

 sented in fig. 4, with an absence of the lines corresponding 

 with the solar H.H lines. This absence was noticeable, also, 



