328 



1855, 37'2. All the stations on the west coast are situated in higher 

 latitudes, yet their mean temperature was in excess of that of Oxford 

 in December 1857 by 2'l ; in the colder Decembers of 1856 and 

 1855, by 0'5 and 1*4 respectively. During the warmest month, the 

 mean of all the coast stations exceeded the temperature of Oxford by 

 2-0; and during the other two Decembers by 1'3 and 1'6 

 respectively. 



I propose to make more complete calculations, which will embrace 

 the other months belonging to the winter; and by comparing the 

 results during different years, it is probable that corresponding infer- 

 ences will be suggested regarding the variations of mean temperature 

 which are incapable of explanation by changes of solar radiation alone. 



I was induced to select December at first, because the amount of 

 sunshine received in our hemisphere being least during that month, 

 it was natural to expect that the comparative effects of the other 

 thermal influences would be most distinctly manifested. 



Having been for some time occupied in studying the distribution 

 of heat over islands, I have been led to the general proposition, that 

 the isothermals may be represented by curves having some relation 

 to the coast-line, and that the positions of the centres of these curves 

 depend upon the relation between solar influence and oceanic tempe- 

 rature. At seasons when the latter becomes important, compared to 

 the former, the isothermals tend to assume re-entrant shapes similar 

 to the mean annual isothermals of Ireland. When the isothermals 

 of a mild winter month, like December of 1857, shall be laid down, 

 I anticipate that they will distinctly exhibit the increased thermal 

 influence of the ocean by presenting such an appearance. 



HENRY HENNESSY. 

 Major-General Sabine, F.P.R.S. 



XVII. " On the Influence of Temperature on the Refraction of 

 Light." By Dr. J. H. GLADSTONE, F.R.S., and the Rev. 

 T. P. DALE, M.A., F.R.A.S. Communicated by Dr. GLAD- 

 STONE. Received June 17, 1858. 



(Abstract.) 



Those who have occupied themselves with the determination of 

 refractive indices, must have noticed that changes of temperature 



