122 



Mr. J. N. Lockyer. 



[Nqv. 17, 



C. Experiments upon Mg at low Temperatures. 



I have again gone over the experiments already communicated to 

 the Royal Society (' Roy. Soc. Proc.,' vol. 30, p. 27), and in addition 

 have observed the spectrum of the metal burning in the centre of a 

 large bunsen burner, in which case we get the line at 5201, and the 

 fluting in the position of b without the fluting at 500. In the bunsen 

 as ordinarily employed the fluting at 500 far eclipses the other parts 

 of the spectrum in brilliancy, and at this temperature, as already 

 observed by Messrs. Liveing and Dewar (' Roy. Soc. Proc.,' vol. 32, 

 p. 202), the ultra-violet line visible is that at 373. Lecoq de Bois- 

 baudran has observed the lines in the chloride at 4705 and 4483 

 (' Spectres Lumineux,' p. 85). 



D. Experiments upon the Glow of Na and Mg in Vacuum Tubes. 



A small piece of sodium, free from hydrocarbon, was placed in the 

 lower limb of an end-on spectrum tube, and arrangements made for 

 observing the spectrum of the gas evolved when the sodium was 

 heated. Having first obtained as perfect a vacuum as possible, the 

 sodium was gently heated, and the spectrum of the gas then gave 

 nothing but the C and F lines of hydrogen. The pump being stopped 

 and the sodium heated, a point was reached when and P became 

 very dim and were replaced by the structural spectrum of hydrogen. 



In another experiment the sodium was replaced by a piece of 

 magnesium along the end-on tube. The same process being gone 

 through, similar phenomena were observed, but in the latter case 

 there was a line at 500, in addition to the lines seen in the case of 

 sodium. 



The important point, then, is the existence of a line at 500 in the 

 spectrum when magnesium is heated, and the absence of such a line 

 in the gas evolved by sodium under the conditions stated. 



E. Experiments upon the Conditions under which the C and F Lines of 

 Hydrogen disappear from the Spectrum. 



The association of the bright lines of hydrogen with nebulas, 

 many of the stars with bright lines, and the so-called new stars, points 

 out at once that it is important to consider the various changes which 

 hydrogen can undergo under various conditions of temperature and 

 pressure. I pointed out many years ago that, when under certain con- 

 ditions the spectrum of hydrogen is examined at the lowest possible 

 temperature, the P line retains its brilliancy long after C disappears ; 

 and the fact that, after the chief lines of hydrogen have been made 

 to disappear from the spectral tube, the spectrum which remains 

 visible, and is sometimes very brightly visible, is also due to hydrogen, 

 has always been a matter of thorough belief in my mind, although so 



