1880.] On the Spectra of Magnesium and Lithium, 



95 



extending, with gradually diminishing intensity, towards the blue . . 

 . . . from forty-five to fifty being visible, and placed at nearly equal 

 distances from each other." 



These observations, though very briefly described, were the result of 

 much labour and many experiments. Mr. Lockyer, in a recent com- 

 munication to the Society, has made this particular emission spectrum 

 the basis of a theory of his own, which we regard as being without 

 any foundation in fact ; and as he makes no allusion whatever to our 

 observations, although the abstract of our paper appeared in various 

 scientific journals,* or to the grounds on which we have ascribed the 

 spectrum to a mixture of magnesium with hydrogen, we give now some 

 further details of our former experiments, as well as the observations 

 which we have made since. 



1, Observations on the Spark between Magnesium Points in Nitrogen 

 and Carbonic Oxide at Various Pressures. 



The points were pieces of magnesium wire. Round one end of 

 each a platinum wire was tightly coiled and fused into the side of a 

 glass tube. This tube was attached by fusion at one end to another 

 tube filled with phosphoric anhydride, which in turn was connected 

 with a Sprengel pump. The other end of the tube was connected 

 by a thick rubber tube, capable of being closed by a pinchcock, with 

 a gas holder containing nitrogen over strong sulphuric acid. The 

 tube, having been exhausted and filled with nitrogen two or three 

 times, it was found that no line at 5210 was visible in the spark. 

 The tube was now gradually exhausted, and the spark watched as 

 the exhaustion proceeded. No line at 5210 was seen, although the 

 exhaustion was carried nearly as far as the pump would carry it ; nor 

 was any hydrogen line (0 or F) visible, either with or without the 

 use of a jar. The communication with the gas holder was now 

 opened, and the tube refilled with nitrogen at the atmospheric 

 pressure, a communication was then made with another vessel con- 

 taining hydrogen, which was allowed to diffuse into the tube for a 

 very short time. On now passing the spark, the line at 5210 at once 

 appeared, although the quantity of hydrogen diffused into the nitrogen 

 must have been very small. The experiments with nitrogen at 

 reduced pressure were repeated several times, with the same result. 

 It was found necessary to have the phosphoric anhydride, as without 

 it traces of moisture were left or found their way through the pump 

 into the tube, and then, when the exhaustion was carried far enough, 

 both the line at 5210 and the hydrogen lines, C and F, made their 

 appearance. We have never, however, been able to detect the line 



* " Nature," vol. xviii, pp. 109, 321. " Proc. Camb. Phil. Soc," vol. iii, Part Y. 

 p. 208. 



