1 '1-2 Royal Societj/. 



he had not succeeded in obtaining numerical results. He 

 found, however, that the refrangibility of the rays diminished 

 with their temperature. 1 also obtained a slight refraction of 

 non-luminous heat through a glass prism. 



1 7. But if heat be capable of refraction by the ordinary 

 agents, an important question arises, Is the phajnomenon of 

 double refraction common to heat and light? Rock-salt, 

 the only substance yet discovered vi'hich transmits dark heat 

 in large quantity, does not possess this power. To attempt it 

 with Iceland spar would certainly be fruitless, from the very 

 small transmitting power which it possesses, besides some 

 other practical difficulties which suggest themselves. It must 

 be by more refined processes that we can detect this property. 

 Such will be stated in the sequel. 



[To be continued.] 



XXIII. Proceedings of Learned Societies. 



ROYAL SOCIETY. 

 1834. A PAPER was read, entitled, " On the Determination 



A 



Nov. 20. — -^^ of the Terms in the disturbing Function of the 



fourth Order, as regards the Eccentricities and Inclinations which 

 give rise to secular inequalities." By J. W. Lubbock, Esq., V.P. 

 and Treas. R.S. 



The author observes, that the magnitude of the terms of the fourth 

 order in the disturbing function, relating to the inclinations, in the 

 theory of the secular inequalities of the planets, does not admit of 

 being estimated d, priori ; and consequently the amount of error 

 which may arise from neglecting them cannot be appreciated. The 

 object of the present investigation is to ascertain the analytical ex- 

 pressions of these terms ; and the method adopted for this purpose 

 is derived from principles already explained by the author in a for- 

 mer paper. He has bestowed great pains in putting these expres- 

 sions into the simplest form of which they are susceptible ; and has 

 finally succeeded, after much labour of reduction, in obtaining ex- 

 pressions of remarkable simplicity. He exemplifies their application 

 by the calculation, on this method, of one of the terms given by Pro- 

 fessor Airy as requisite for the determination of the inequality of 

 Venus ; and arrives, by this shorter process, at the same result. The 

 same method, he remarks, is, with certain modifications, applicable 

 to the development of the disturbing function in terms of the true 

 longitude. 



A paper was also read, entitled " Note on the Astronomical Re- 

 fractions." By James Ivory, Esq., K.H., M.A., F.R.S. 



The object of this communication is to show how far the author 

 has been successful in establishing the true theory of astronomical 

 refractions, in his paper published in the Philosophical Transactions 

 for 1823, by comparing the results of that theory with the best and 

 most recent observations ; namely, those recorded in the " Funda- 



