370 Prof. Challis on the Theory of the Moon's Motion. 



Diluted sulphuric acid, sp. gr. 1*0682, does not dissolve it at 

 the ordinary temperatures, but does so readily with the aid of 

 heat. Sulphuric acid, sp. gr. 1*845, rapidly dissolves it. 



Diluted hydrochloric acid has but little action on it, but when 

 concentrated, it almost instantly reddens, without dissolving it; 

 upon boiling, it forms a yellow solution, from which minute, 

 dark, opake, radiating aciculse deposit on cooling. 



Nitric acid immediately decomposes it, even in the cold ; upon 

 raising the temperature, iodine at first volatilizes ; then nitrous 

 acid vapours are evolved. Iodine is probably partially converted 

 into iodic acid. 



Hydro-sulphuric acid passed through its alcoholic or acetic acid 

 solution at once decomposes it, converting the iodine into hy- 

 driodic acid, with separation of sulphur. 



Alkalies and alkaline earths in solution at once decompose it, 

 removing the sulphuric acid and leaving a Naples yellow residue 

 containing the quinine and a portion of the iodine ; a soluble 

 iodide of quinine is also formed in ammoniacal liquids. 



LIU. The Theory of the Moon's Motion. — Results of a Third 

 Approximation. By the Rev. Professor Challis, M.A.,F.R.S.* 



IN two previous communications I have shown in what man- 

 ner terms that may increase indefinitely with the time are 

 introduced into the development of the radius-vector, and what 

 processes are proper for avoiding them. That this is an import- 

 ant point in the lunar theory is evident from the circumstance, 

 that the occurrence of such terms has in a great measure regu- 

 lated the course which the solution of the problem has taken. 

 It has been thought necessary, in order to get rid of them, to 

 introduce a priori into the investigation expressions suggested 

 by the observed motions of the nodes and apses of the moon's 

 orbit. (See Pontecoulant, Theorie de la Lune, Chap. I. No. 5.) 

 But it is certain on general principles that there must be a course 

 of reasoning by which the expressions appropriate to the problem 

 may be developed without the necessity of any assumption re- 

 specting their form ; and as the solution I have commenced in 

 this Magazine appears to be of this kind, I propose now to carry 

 it on to a higher approximation. Although this method may 

 lead to no numerical results differing in any sensible degree from 

 those already obtained, I cannot but think that it is worth while 

 to give to a problem of so great interest and importance as logical 

 a solution as possible. 



For the sake of clearness, I shall first recapitulate the previous 



* Communicated by the Author. 



