Mr. Ivory 07i the Theory of the Astronomical Refractions. 3 



diameter. It is almost unnecessary to add, that the combus- 

 tion must be very slowly conducted. 



During the whole of the analysis, a quantity of oxygen gas 

 is disengaged from the potash apparatus, which arises from 

 the great predisposition of the chromate of lead to be con- 

 verted into a basic salt. This fact, with the great quantity 

 of oxygen which the salt contains, renders it very advanta- 

 geous in the combustion of those bodies which contain a 

 large quantity of carbon, and are difficult to consume. With 

 this salt a much larger quantity of substance can be submitted 

 to analysis than with oxide of copper, arising from its greater 

 specific gravity. It is also an excellent means of analysing 

 bodies containing chlorine, bromine, &c., the chloride, bro- 

 mide, &c. of lead not being volatile. 



For the suggestion of the employment of this body in or- 

 ganic analysis we are indebted to Prof. Liebig. 



The following analysis was made with the view of testing 

 its accuracy: '8166 grm. of ordinary sugar, gave 1'24<1 grm. 

 COg, and -4725 grm. HgO, which produces in 100 parts, 



Theory. 



Carbon; 42-02 42-403 



Hydrogen 6-40 6-390 



Oxygen 51-58 , 51-207 



100-00 100-00 



III. The Balccrian luccture. — On the Theory of the Astrono- 

 mical Refractions. By James Ivory, K.H., M.A., F.R.S. 

 L. 4" -E., Instit. Reg. Sc. Paris, Corresp, et Reg. Sc. GottiJi. 

 Corresp. 



[Continued from vol. xiv. p. 352.] 



6. TN the paper published in the Philosophical Transac- 

 ■^ tions for 1823, the refractions are deduced entirely 

 from this very simple formula, 



i±|i, = i-/(i-c-) {*.) 



in which /3 stands for the dilatation of air, or a gas, by heat ; 

 T is the temperature at the earth's surface, and t the tem- 

 perature at any height above the earth's surface ; at the same 

 height c"" is the density of the air in parts of its density at 

 the surface. 



In order to understand the application of the formula, it is 

 necessary to premise that in the remaining part of this paper 

 we do not consider a variable atmosphere subject to continual 

 fluctuations, as is the case of the real atmosphere : we con- 



B2 



