258 REPORT— 1880. 



Report of the Coriimittee, consisting of Professor Dewar, Dr. 

 Williamson, Dr. :M.\i!.snALL Watts, Captain Abney, Mr. Stoxey, 

 Professor Hartley, Professor McLeod, Professor Carey Foster, 

 Professor A. K. HuxTiNGTOif, Professor Emersox Reynolds, Pro- 

 fessor Reinold, Professor Liveing, Lord Eayleigh, Dr. Schuster, 

 and Mr. W. Chandler Roberts (Secretary), appointed for the 

 purpose of repjortlag upon the. present state of our KnovJedge 

 of Spectrum Atudysis. 



[Plates X. axd XL] 



Coiitciitii. 

 § 1. Spectra of Metalloids (drawn up by Dr. Schuster). 

 § 2. Influence of Temperature and Pressure on the Spectra of Gases (drawn up b\ 



Dr. Schuster). 

 § ?,. Emission Spectra of the Kays of High Refrangibility (drawn up by Prof. Hartley). 

 § 4. Absorption Spectra of the Hays of Hioh Kefrangibility (drawn up by Prof. 



Huntington). 



§ 1. Spectra of Met.'vllgids. By Dr. Schuster, F.B.S. 

 I. Preliminary RemarJcs. 

 Certain spectroscopic changes and variations, wliich we now know to bc- 

 common botb to metals and metalloids, were first observed in the case of 

 metalloids. It is owing to this fact tliat their spectra have given rise to 

 so much discussion. Angstrom and v. d. Willigen had examined electric 

 sparks passing through various gases, and had thus observed the spectra 

 of several metalloids ; but the subject first received due attention when 

 Plucker and Hittorf (1804) announced the important discovery that one 

 and the same element can, under different conditions, show more than one 

 spectrum.' Attempts were naturally made to disprove such a remarkable 

 and at first sight improbable assertion. DiSerent spectroscopists took 

 different views ; most metalloids were carefully examined, and in the long 

 dif^cussion which followed, each side had to give in on some points. 

 Pliicker's discovery, however, was established in the case of all metalloids 

 Avhich have been sufficiently well studied. There is now among those 

 best able to judge a general agreement on the facts, although great diffei-- 

 ences exist as to their interpretation. We have in the present Report 

 nothing to do with the explanations which have been offered to account 

 lor the variability of spectra, but only to record facts and to desci'ibe the 

 phenomena which appear when the spectra of metalloids are examined 

 under different and varying conditions. 



It is perhaps advisable to say one word on the nomenclature which 

 we shall adopt, and on the general appearance of the spectra with which 

 we have to deal. Different spectra often resemble each other in 

 general appearance, so that we can classify and roughly divide them into 

 three kinds or orders : continuous spectra, line spectra, and spectra of 

 Anted bands, or channelled-space spectra, as they are sometimes called. 

 Piiicker and Hittorf called the spectra of fluted bands, spectra of the first 

 Older ; the line spectra, spectra of the second order. This nomenclature 



' Both Plucker and v. d. Willigen had already, in 1858, described the band spec- 

 trum of nitrogen, but the sultject was first tlioroughly investigated by Piiicker and 

 Hittorf, and only received due attention after the publication of their paper. 



