﻿94 Miss Ellen O'Connor on the Spectrum of 



the problem of uniform translation, however, it certainly 

 seems that we must either introduce a sufficient number of 

 what we have termed subsidiary laws, to completely restrict 

 the moving system to one type in its relation to the fixed 

 system, quite apart from the consideration as to whether the 

 motions in it could have arisen out of the fixed system, or, 

 must specify completely the state of the field, and consequently 

 of the electronic motions in the system at rest, and also the 

 exact electromagnetic procedure by which the translatory 

 motion is imparted, for in the general case the final result 

 will depend on these *. Specification of the electronic 

 motions in the system at rest corresponds in part to a state- 

 ment of the elastic properties of the material, and the deter- 

 mination of the solution of our problem without specification 

 of these motions would be, in general, as impossible, as would 

 be the determination of the extension of an elastic thread 

 when swino-ing round with a weight at the end, if we were 

 without knowledge of the elastic properties of the thread. 



The University of Sheffield, 

 June 30, 1911. 



VII. On the Spectrum of the Magnesium High-frequency Arc. 

 By Ellen O'Connor, B.Sc.j 

 [Plate V.] 



FTpHE element magnesium shows, probably to a greater 

 I extent than any other element, changes in the spectrum 

 according to the various means adopted for bringing the 

 substance into the state of incandescent vapour. This and 

 also, as Kayser points out, its astronomical importance have 

 led to numerous investigations on the behaviour of magnesium 

 under varied conditions of electrical discharge. The high 

 frequency discharges hitherto emplo} T ed depend upon the 

 oscillatory discharge of a leyden-jar, and are therefore of 

 the nature of damped oscillations. The electrical conditions 

 in such a discharge are very complex and not yet fully 

 understood. It seemed of interest, therefore, to examine 

 the spectrum of an undamped oscillatory discharge such 

 as can now be produced by the methods employed in 

 wireless telegraphy. 



Apparatus. — The generator employed was of the Poulsen 



* Ordinary electro-dynamical principles, involving- the conception of 

 forces between the singularities, make the effects produced in the system, 

 bv the translatory motion, depend on the electronic motions in the system 

 at rest, the solution corresponding to that given by the transformation 

 only following as an approximation, for the case of very slow orbital 

 motions. 



f Communicated by the Author. 



