59 



distances of the plates, and also the distance of the gold leaves from 

 one another, new conditions are supplied for the more exact deter- 

 mination of the relative inductive powers of dielectrics of every de- 

 scription ; and by sufficiently reducing the dimensions of the instru- 

 ment, it may be rendered applicable to comparatively small masses 

 of dielectrics, such as crystals, and even diamonds. An instrument 

 capable of such universal application the author proposes to desig- 

 nate by the name of Differential Inductometer. 



Also read, a Letter addressed to P. M. Roget, M.D., Secretary 

 to the Royal Society, by James Ivory, Esq., F.R.S., accompanying 

 a paper on Astronomical Refractions. Communicated by Dr. Roget. 



The author adverts in this letter to the attempts made by New- 

 ton to solve the problem of atmospherical refractions, which were 

 baffled by the experience that the observed quantities fall far short 

 of the theoretical deductions ; whence he justly inferred that some 

 new cause must be sought for capable of effecting that change in 

 the density of the lower part of the atmosphere which is required for 

 reconciling theory with observation. It becomes necessary, in par- 

 ticular, to investigate the law according to which the temperature 

 diminishes as the height increases. The initial value of the rate of 

 diminution has to be determined by experiment ; and the introduc- 

 tion of this new element into the equation of an atmosphere in equi- 

 librium must be an approach to the true solution of the problem of 

 the refractions, and is indispensable if arbitrary assumptions are to 

 be avoided. The author proceeds to notice Laplace's solution, 

 which, though highly ingenious, is nevertheless hypothetical ; and 

 he adverts to the want of precision exhibited in Biot's dissertation 

 on the influence which the presence of aqueous vapour in the air 

 has on the refractions : but refers to the paper which accompanies 

 his letter for the further explanation of his views on this subject. 



A paper was also in part read, entitled, *' On the Theory of the 

 Astronomical Refractions," by James Ivory, Esq., K.H., M.A., 

 F.R.S., &c. 



May 10, 1838. 



FRANCIS BAILY, Esq., V.P. and Treas.,in the Chau". 



llie reading of Mr. Ivory's paper *' On the Theory of Astronomi- 

 cal Refractions," was resumed. 



The Society then adjourned, in consequence of the 17th having 

 been fixed for celebrating Her Majesty's Birth-day, to meet again 

 on the 24th instant. 



