208 THE ROYAL SOCIETY OF CANADA 



It will be seen that while there is agreement for five or six wave- 

 lengths in the values found by the two methods there are a number of 

 wave-lengths recorded photographically that were not detected by the 

 cell method. Similarly a number of wave-lengths were detected by 

 the cell method of which no trace was obtained photographically. 

 It seems evident, too, both from the photographic record and the 

 readings taken with the cell that the wave-length usually given at 

 X=10140A is in reality a combination of wave-lengths with strong 

 members at X = 10121A and X = 10165A. 



Part II. Infra-red Spectra of Certain Metals 

 (1) Introduction 



In this part of the investigation an attempt was made to study 

 by the photographic method the infra-red spectra of tin, lead, bismuth, 

 zinc and antimony. 



While many of the early workers in spectroscopy had studied 

 the infra-red spectra of various metals it is to such workers as Paschen 

 and Randall that we are primarily indebted for accurate determina- 

 tions of wave-lengths in the spectra of many of the elements in the 

 near infra-red region. 



Some notable work was done by Paschen^ in 1909, partly with a 

 bolometer and partly by photography, in the infra-red region extend- 

 ing up to X28000A. In the following year he extended his observa- 

 tions to X 50000A. By phosphor-photography Lehmann^ successfully 

 measured a number of infra-red lines in the spectra of various metals. 

 As regards the spectrum of bismuth it may be pointed out that 

 experiments have been made on it by A. Kretzer,^ that are worthy 

 of special mention. 



Extensive infra-red measurements (probably the most reliable 

 and comprehensive of their kind, of recent date) have been made by 

 H. M. Randall,* who examined the spectra of eleven elements in the 

 region X 7500A to X 30,000A. A carbon arc was used as a source of 

 light, the lower positive carbon having been bored out and filled with 

 the material to be examined. The light was focussed by a quartz 

 lens on the slit of the spectrograph which, including the concave 

 mirror, Rowland grating and thermopile was enclosed in a thick 

 walled chamber of brass. The thermopile used was of the Rubens 



iPaschen, Ann der Phys. 29, p. 625, 1909; 27, p. 537, 29, 625, 33, 717, 1910. 



^Lehmann, Ann. der Phys. 39, p. 53, 1912. 



«Kretzer, Zeit. Wiss. Phot. 8, p. 45, Jan., 1910. 



*H. M. Randall, Astrophys Jl. Vol. 34, No. 1, July, 1911. 



