456 BEPOBT — 1880. 



known B group, having a close resemblance in general character to the series of 

 lines produced by an electric discharge in a vacuum tube of olefiant gas. 



The series appears at all temperatures except when a large condenser is em- 

 ployed along with the induction coil, provided hydrogen is present as well as 

 magnesium, while they disappear when hydrogen is excluded, and never appear in 

 dry nitrogen or carbonic oxide. ^ 



From their experiments on carbon spectra they conclude with Angstrom and 

 Thalen that certain of the so-called ' carbon bands ' are due to some compound of 

 carbon with hydrogen, probably acetylene, and that certain others are due to a 

 compound of carbon with nitrogen, probably cyanogen. 



They describe some ultra-violet bands : one of them coincides with the shaded 

 hand P of the solar spectrum which accompanies the other violet bands in the 

 flame of cyanogen as well as in the arc and spark between carbon electrodes in the 

 nitrogen. All the bands which they ascribe to a compound of carbon and nitrogen 

 disappear when the discharge is taken in a non-nitrogenous gas, and they reappear 

 on the introduction of a minute quantity of nitrogen. 



They appear in the flame of hj-drocyanic acid, or of cyanogen, even when 

 cooled down as much as possible as shown by Watts, or when raised to the highest 

 temperature by burning the cyanogen in nitric oxide ; but no flames appear to 

 give these bands unless the burning substance contains nitrogen already united 

 with carbon. As the views of Mr. Lockyer with regard to the multiple spectra of 

 carbon have very recently appeared in the pages of ' Nature,' I need only say that 

 these spectra are looked upon as supporting his theory that the diffei-ent flutings 

 are trulj^ due to carbon, and that they represent the vibrations of difl'erent molecular 

 groupings. The matter is one of very great interest as regards the spectra of comets, 

 for the bands ascribed to acetylene occur in the spectra of comets without the bands 

 of nitrogen, showing that either hydro-carbons must exist ready formed in the 

 comets, in which case the temperature need; not exceed that of an ordinary flame, 

 or else nitrogen must be absent, as the temperature which would produce acetylene 

 from its elements would also produce cyanogen, if nitrogen were present. 



Quite recentlj'. Professors Li^eing and Dewar have, simultaneously with Dr. 

 Iluggins, described an ultra-violet emission spectrum of water, and have given maps 

 of this spectrum. It is not a little remarkable that by independent methods these 

 observers should have deduced the same numbers for the wave-lengths of the two 

 strong lines at the most refrangible end of this spectrum. 



Great attention has been paid by M. Mascart and by M. Oornu to the ultra- 

 violet end of the solar spectrum. M. Mascart was able to fix lines in the solar 

 spectrum as far as the line R (3170), but was stopped by the faintness of the 

 photographic impression. Professor Oornu has extended the spectrum still farther 

 to the limit (2948), beyond which no further effect is produced, owing to complete 

 absorption by the earth's atmosphere. A quartz-reflecting prism was used instead 

 of a heliostat. The curvature of the quartz lens was calculated so as to give mini- 

 mum aberration for a large field of view. The Iceland spa prism was very care- 

 fully cut. A lens of quartz was employed to focus the sun on the slit. Ha\"ing 

 photographed as far as possible by direct solar light, Professor Oornu compared the 

 solar spectrum directly bj' means of a fluorescent eyepiece with the spectrimi of 

 iron, and then obtained, by photography, the exact positions of the iron lines 

 which were coincident with observed lines in the solar spectrum. M. Oornu states 

 that the dark absorption lines in the sun and the bright iron lines of the same 

 refrangibility are of the same relative importance or intensity in their spectra, indi- 

 cating the equality between the emissive and the absorbing powers of metallic 

 vapours ; and he thinks that we may get by the comparison of bright spectra with 

 the sun some rough approximation to the quantity of metallic vapours present in 

 the absorption layers of the sun's atmosphere. He draws attention to the abun- 

 dance of the magnetic metals — iron, nickel, and magnesium — and to the fact that 

 these substances form the composition of most meteorites. M. Oornu has studied 

 the extent of the ultra-violet end of the spectrum, and finds that it is more extended 

 in winter than in summer, and that, at different elevations, the gain in length of 

 the spectrum for increase of elevation is very slow, on account of atmospheric absorp- 



