*24T» J. Trowbridge — Gaseous Constitution of the 



of silicon, in air; and one might conclude that the lines come from 

 a volatilization of the walls of the quartz capillary. There is, 

 however, absolutely no corrosion of the walls of the quartz vessel. 

 The surface of the quartz remains limpid and clear. Fig. 3 

 shows the same lines, wave lengths 2882, and group from 2542 

 to 2507. In fig. 3 these lines are not reversed and there is no 

 continuous spectrum. The argument of incandescent walls to 

 account for the continuous spectrum in the case of glass tubes 

 would require a heat of incandescence to volatilize the silicon 

 to produce the bright lines seen in fig. 3. I have concluded 

 that, just as in the case of the supposed calcium lines with 

 the employment of glass tubes, these reversed lines are also due 

 to a gas. In order to discover whether these lines can be 

 obtained from some gaseous constituent of the air, I have 

 studied the spectra obtained from powerful sparks in air taken 

 from a great variety of metallic terminals. The spectra from 

 terminals of pure platinum, electrolytic silver, and iridium show 

 strong lines, which coincide with the dispersion I have employed, 

 with the great H.H. lines of the solar spectrum and also with 

 the gaseous lines I have obtained in rarih'ed hydrogen. Ter- 

 minals of aluminum, copper, iron, tin, magnesium, do not show 

 these lines, or if at all, very faintly. The noble metals, which 

 are least affected by the electric discharge and which are there- 

 fore used for nonoxidizable contact in electric apparatus, give 

 these lines. Is it not probable that when the electric discharge 

 volatilizes to a high degree the electric discharge prefers a pas- 

 sage through the metallic vapor — that is, when short and power- 

 ful condenser discharges are employed — and does not sufficiently 

 heat the air to bring out certain air lines. The method of 

 sifting out air lines from metallic spectra by observing the lines 

 which are apparently common to these spectra and setting down 

 such lines as air lines, is a fallacious method. Silicon is not 

 easily volatilizable and certain important groups of lines attrib- 

 uted to that metal, obtained by the use of the spark in air, 

 may be atmospheric lines. I have obtained traces of such lines 

 which seem to coincide with the gaseous lines I obtained with 

 rarified hydrogen in quartz tubes by employing water electrodes. 

 These electrodes were made as follows : two iridium terminals 

 were placed on pieces of kiln-dried wood four inches apart. 

 The condenser spark could leap only one inch. The wood was 

 wrapped with cotton enclosing the metallic terminals ; around 

 the cotton was wrapped chamois skin; the clear space, between 

 the ends of the wood, thus protected, was half an inch. The 

 terminals thus prepared were soaked in distilled water. A very 

 powerful spark was thus obtained in air : and the spectrum was 

 entirely free from metallic lines. With these terminals it is 

 undoubtedly true that the water vapor conducted the main body 



