466 Mr. H. Wilde on Helium and its place in the 



The absolute value of the illumination at the point G due 

 to the source L is equal to the illumination which would be 

 produced if L were removed and a source of candle-power 

 represented by MK on the same scale as LD were placed at M. 



In order to show the applicability of the method, three 

 photometer-curves are shown in figures 1, 2, and 3 ; the first 

 being due to an Argand burner without shade, the second the 

 same burner with a conical paper shade (from Dibdin's 

 ' Photometry '), the third to an arc lamp (from Trotter's 

 paper in the Journal Inst. Elect, vol. xxi. p. 365, 1892), and 

 the illumination produced by each source on a horizontal 

 plane is found *. 



It is interesting to notice the great increase of illumination 

 in the case of the Argand burner when the shade is introduced. 

 In the case of the arc, the point on the horizontal when the 

 illumination is a maximum is evidently at about 60° below 

 the horizontal plane through the lamp. 



XLI. On Helium and its place in the Natural Classification 

 of Elementary Substances. By Henby Wilde, F.R.S.'t 



[Plate VIII.] 



THE announcement made by Professor Ramsay that a gas 

 from the mineral Cleveite showed the yellow spectral line 

 of solar helium A. 5876, and was therefore identical with that 

 hypothetical element J, was received by physicists with some 

 amount of incredulity, as it was illogical to predicate the 

 identity of any element from the near coincidence of a single 

 line among the numerous lines which belong to other elemen- 

 tary substances in the gaseous condition. Nevertheless, the 

 conspicuous brightness and comparative isolation of the chro- 

 mospheric line D 3 , together with the statement by Crookes, that 

 the yellow line of the cleveite gas was single §, in agreement 

 with the reputed singleness of D 3 , gave some force to the idea 

 that the solar and terrestrial gases were identical. Lockyer || 

 and RungeH, however, subsequently discovered that the yellow 

 line of the new gas was double, and the latter observer justly 

 remarked " that the unknown element helium, causing the 

 line D 3 to appear in the solar spectrum, is not identical with 

 the gas in cleveite unless D 3 is also shown to be double." 



* These curves have been kindly drawn for me by Mr. Julius Frith, 

 Exhibition (1851) Scholar of the Owens College. 



t A paper read before the Manchester Literary and Philosophical 

 Society, October 1, 1895. Communicated by the Author. 



\ Chemical News, March 29, 1895. § Ibid. p. 151. 



j| Proc. Roy. Soc. April 25, p. 69. 



II Nature, June 6, p. 128. 



