1 Wright and Downs — Spectrum of the 



In the next experiment platinum electrodes were used in 

 order to determine whether the lines were due to copper or to 

 the gases through which the discharge passed. This plate upon 

 development showed exactly the same series of sharp lines. 

 Hence they must be due to some one of the gases, or the oxides 

 of them, which occupy the intra-polar space. 



To settle the location of the lines conclusively the camera 

 was adjusted so as to include the region in the first spectrum 

 in which they were supposed to be. An ordinary dry plate 

 without staining was used and an exposure of an hour given it. 

 After the development of the plate the lines sought were seen 

 sharp and clear, which proved conclusively that they were in 

 the ultra-violet of the first spectrum. 



The work of ascertaining to what one of the intra-polar gases, 

 or oxides of them, the lines belonged, was next taken up. A 

 careful comparison of the recorded lines of the hydrogen spec- 

 tra did not reveal any coincidence. In the Report* -of the 

 British Association for the Advancement of Science some lines 

 due to water vapor are given, and a comparison with the lines 

 studied in this investigation showed that a large number of 

 them were apparently in exact coincidence. 



These lines were discovered by W. Hugginsf and also by 

 Gr. D. Liveing and J. DewarJ at almost the same time. Hug- 

 gins exposed a photographic plate to the flame of hydrogen 

 burning in air for one minute and a half and was very much 

 surprised upon developing it to find such a strong group of 

 lines. He traced the lines in this group from wave lengths 

 3062 to about 3290, the upper limit of which is about the same 

 as that of the lines studied here and the lower limit consider- 

 ably below. Upon placing a spirit lamp before the slit of the 

 spectroscope the spectrum is essentially the same, but, as it is 

 less intense, only the strongest lines are seen. 



In their article Liveing and Dewar give the results of the 

 study of some lines which they had obtained and noted in the 

 spectrum of coal gas burning in oxygen when investigating the 

 spectrum of " Compounds of Carbon with Hydrogen and 

 Nitrogen." The group of lines which they obtained extends 

 from wave lengths 3062 to about 3210. The same spectrum 

 was given by the electric spark taken, without condenser, in 

 moist hydrogen, oxygen, nitrogen, and carbonic acid gas, but 

 it disappeared if the gas and apparatus were thoroughly dried. 

 Hence they were led to the conclusion that the spectrum was 

 that of water. In conclusion they were not prepared to guar- 

 antee that oxides of nitrogen from traces of air might not have 

 something to do with some parts of the spectrum here observed. 



*1886, p. 169. fProc. Roy. Soc, vol. xxx, p. 576. 



% Proc. "Roy. Soc , vol. xxx, p. 580. 



