50 Rev. T. Pelham Dale on the Upper Limit 



pendent matter, not involved in MaxwelFs dielectr'c theory, 

 though perhaps needing consideration in some other theory. 

 But the moment we let the electric current have divergence 

 (the absence of which makes the vortex-lines of e to be the 

 sources of disturbances), we at once (in my experience) get 

 lost in an almost impenetrable fog of potentials. Maxwells 

 theory unamended, on the other hand, works perfectly and 

 without a trace of indefiniteness, provided we regard E and H 

 as the variables, and discard his " equations of propagation " 

 containing the two potentials. 

 October 22, 1888. 



V. On the Upper Limit of Refraction in Selenium and Bromine. 

 By Rev. T. Pelham Dale, M.A* 



IN jny former paper read before the Society f I showed that 

 the value of the limit could be found by the solution of 

 the equation 



a sin 6=. sin m^ ; 



7 



where a is the ratio of wave-lengths in free sether, and 6-=- -y-' 



h being what I there called the molecular distance, and I the 

 corresponding wave-length within the medium. If a sin 6 be 

 greater than unity, the solution is imaginary. 



It was also shown that if v be limit of refraction, //, the 

 index corresponding to 6, that 



ijb sin 6 

 =1/ 



d ' 



If ^= 77, we have 



^=-2'^'" 



/i being the index of the limit of refraction towards the violet 

 end of the spectrum. Call this the upper limit, and denote it 

 by ^lk• 

 .'. fik—v is the total dispersion 



also \2 / ' 



^-^y — = constant independent of temperature. 



Also by the relation 



* Communicated by tbe Physical Society : read November 10, 1388. 

 t Phil. Mag. May 1888, p. 325. 



