Rev, J. Challis on the Motion of Fluids. 7 



on this branch at all prepared for publication. A paper of 

 his, published in the Transactions of the Geological Society, 

 contains very valuable contributions towards the history of 

 our fossil Belemnites, and has been most favourably referred 

 to by the French author who has subsequently published the 

 standard monography of that department. 



Mr. Miller's talents have been highly estimated by the 

 ablest of our naturalists and geological writers. Professor 

 Blumenbach, Baron Cuvier, MM. Latreille and D'Aubigne, 

 have expressed in letters to him high commendation of his 

 works. Professor Buckland obtained his assistance in ar- 

 ranging the valuable collection of organic remains belonging 

 to the Ashmolean Museum at Oxford. The same Professor, 

 in his very interesting paper 'on the recent discovery in this 

 country of fossil remains belonging to the flying reptile the 

 Pterodactylus, mentions that Mr. Miller first suggested to him 

 the possibility, thus confirmed, that the fossil bones commonly 

 supposed to belong to birds really appertained to that animal. 

 And Mr. Conybeare, while drawing up the lists of the organic 

 remains in our strata, which are given in his " Outlines," was in 

 the common habit of appealing to Mr. Miller's authority. 



In surveying the results of Mr. Miller's scientific acquire- 

 ments and of his exertions, we must not forget the important 

 benefits rendered by him to the Museum of the Institution of 

 which he was Curator. It may safely be affirmed, that the 

 history of similar collections does not present another instance 

 in which so rapid a progress has been made in accumulating 

 the varied stores connected with such undertakings ; and the 

 rapidity of this progress must undoubtedly be ascribed in a 

 great measure to the energy and zeal of the Curator in the 

 service, and to the interest which he so well knew how to 

 communicate to those with whom he came into intercourse. 



III. On the theoretical Determination of the Motion of Fluids. 

 By the Rev. J. CHALLIS, Fellow of Trinity College, Cam- 

 bridge, and of the Camb. Phil. Soc.* 



CUPPOSE x,y, z, to be the coordinates of any particle of 

 ^ a fluid mass in motion, at a given time /, and 21, v, w, the 

 velocities of the particle in the directions of the axes of x,y, z, 

 respectively, at that time. The general investigation of the 

 motion of fluids conducts to a case of very extensive applica- 

 tion, in which udx + vdy + wdz is a complete differential of 

 a function of x,y, z, which may also contain t. In a commu- 



* Communicated by the Author. 



nication 



