Mr. W. M. Hicks. 



[June 21, 



within the experimental errors of measurement of identical lines. 

 Professors Liveing and Dewar took the lines which they mapped from 

 sparks passed " between poles of purified graphite in air, carbonic 

 acid gas, hydrogen, and coal-gas. The same lines have been observed 

 in photographs of the spark between iron, and between aluminium 

 poles in carbonic acid gas." " The graphite was purified by being 

 stirred in fine powder into fused potash, and subsequent treatment 

 with aqua regia, by prolonged ignition in a current of chlorine, and 

 by treatment with hydrofluoric acid." " Notwithstanding the purifi- 

 cation the photographs of the spark between these electrodes still 

 showed very distinctly the lines of magnesium and iron." 



From these quotations it will be seen with what great care the 

 preparations for these observations on the carbon spectrum were 

 made. If the poles employed had been those of graphite only, I 

 should have had little hesitation in attributing the seven lines to the 

 silicon spectrum, but they were replaced by iron and by aluminium. 

 Even the purest iron wire contains small traces of silicon, and 

 aluminium of the usual commercial quality certainly contains a con- 

 siderable quantity. There is, therefore, a suspicion that the carbon 

 spectrum was contaminated by silicon, for a series of seven consecutive 

 lines so nearly coincident with those in the spectrum of another 

 element of the same class would be very remarkable. 



II. " On the Steady Motion of a Hollow Vortex." By W. M. 

 HiGKS, M.A., Fellow of St. John's College, Cambridge. 

 Communicated by J. W, L. Glaisher, M.A., F.R.S. Re- 

 ceived May 31, 1883. 



(Abstract.) 



The investigation to which this refers forms a continuation of some 

 researches commenced about three years ago, but which the author 

 was compelled by other engagements to lay aside. The general 

 theory of the functions employed was published in the " Transactions 

 of the Royal Society" (Part III, 1881), under the title of " Toroidal 

 Functions." These and analogous functions are employed in the 

 present communication. 



The interest of investigations of the properties of small vortices 

 •depends on their connexion with the vortex atom theory of Sir W. 

 Thomson, and it was this and the further connexion with a gravitation 

 theory which induced me originally to undertake the investigation. 

 So far as I am aware, very little has been done towards a quantitative 

 theory of vortices beyond the paper ' ' On the Vibrations of a Vortex 

 Hing " by Mr. J. J. Thomson, published in the " Transactions " of this 



