26 Prof. Challis on the Principles of Hydrodynamics. 



composition with nitrate of silver, was found to contain 60*49 per 

 cent, oxide of silver. The calculated quantity of oxide of silver 

 in butyrate of silver, is 59"48 ; that in acetate of silver, 69*46 ; 

 and in metacctonate of silver, 64*09 per cent. It appears highly 

 probable, therefore, that the excess of oxide of silver found in 

 the butyrate arose from a slight admixture of either acetic or 

 metacetonic acids. 



A silver salt was also prepared by digesting oxide of silver 

 with pure acetic acid from the Fuci. It had all the characters of 

 acetate of silver; and when subjected to analysis, 0*250 of the 

 salt gave 0*161 metallic silver =0*172 oxide of silver =69*16 

 per cent ; the calculated amount of oxide of silver in the acetate 

 being, as was previously stated, 69*46 per cent. 



Glasgow, Nov. 26, 1850. 



IV. On the Principles of Hydrodynamics. By the Rev. J. Chal- 

 lis, M.A., F.R.S., F.R.A.S., Plumian Professor of Astronomy 

 and Experimental Philosophy in the University of Cambridge^. 



THE Number of the Philosophical Magazine for last March 

 contains some observations by Professor P. Tardy of Mes- 

 sina, the object of which is to prove that a new general equation 

 in Hydi'odynamics, which I fii*st pointed out, is neither uecessaiy 

 nor trae. In the next Niimber I answered completely, as I con- 

 ceive, the arguments which had reference to the truth of the 

 equation ; and I showed also, that, according to Professor Tardy's 

 own reasoning, a new general hydrodynamical equation is neces- 

 sary. I have not since seen any additional obsei*vations by Pro- 

 fessor Tardy. The views on the principles of hydrodynamics 

 which I have for a considerable time maintained, have now been 

 subjected to the criticisms of several eminent mathematicians, 

 from which I willingly acknowledge that I have derived assistance 

 in my hydrodynamical researches. At the same time I must con- 

 tend that no argument directed against the principles of the new 

 mathematical reasoning* which I have applied to this subject, has 

 remained unanswered, and that the correctness of those prin- 

 ciples is in no respect invalidated. Under the conviction that 

 they are true, and that they cannot be dispensed with, I propose 

 now to adduce, in logical sequence, the vai'ious important results 

 which I have derived from them in different Numbers of this 

 Joui'nal, and to support those results by adcUtional arguments. 

 For the purpose of facilitating any discussion to which the sub- 

 ject may give rise, the reasoning is carried on in separate propo- 

 sitions, and each proof is preceded by a distinct enunciation of 

 the proposition to be proved, 



* Communicated by the Author. 



