84< Prof. Challis on investigating generally the -partial 



have been found in various places, in beds between the chalk 

 and new red sandstone. These were generally so small and 

 badly characterized, that I found it difficult to determine the 

 genus to which they belonged. Within the last few months, 

 however, some well-marked remains have been discovered. 

 They were found in the lower greensand at Woodburn near 

 Carrickfergus, by Mr. Wm. Young of this town ; and consisted 

 of a large dorsal vertebra and some smaller ones from the 

 extremities, but in such a position as rendered it doubtful 

 whether they belonged to the same individual. They were 

 easily recognized to be vertebrae of an Ichthyosaurus, by the 

 compressed form of the body, the double concavity of the 

 articulating surfaces, by the small pits on each side of the 

 spinal canal, and by the articulating tubercles for the attach- 

 ment of the bifurcate rib. The length of the largest vertebra 

 is an inch and a half, and the diameter of its end four inches. 



So far as I am aware, this is the only instance yet recorded 

 of the discovery of Ichthyosaurian remains in this country. 

 In this case, and in that referred to above, the discoveries wei'e 

 due to the zeal and the knowledge of two young gentlemen, 

 who were inspired by myself with a love for this delightful 

 study; and this circumstance, while gratifying to me, is one 

 of the many arguments which might be adduced in favour of 

 turning the attention, at an early period, to the cultivation of 

 the " Science of Observation." 



Belfast, Jan. 20, 1842. 



XV. On the Method of investigatifig generally the partial Dif- 

 ferential Equations applicable to the Motion of Fluids. By 

 the liev. James Cpiallis, M.A., Pliimian Professor of Astro- 

 nomy and Experimental Philosophy in the University of Cam- 

 bridge'^. 

 I PROPOSE in this communication to generalize the me- 

 thod I employed in the Number of this Journal for last 

 September (S. 3, vol. xix. p. 229), in the solution of a pro- 

 blem of hydrodynamics. Although that solution has not re- 

 ceived the assent of a distinguished mathematician, I do not 

 despair of eventually' establishing the correctness of my views, 

 and showing the necessity of their being adopted before any 

 considerable advance can be made in the mathematical theory 

 of fluid motion. It is very possible that in entering upon a new 

 train of reasoning I may have failed to place it in the clearest 

 point of view ; and, in fact, I am now prepared to point out 

 the source of some portion of the obscurity. I have argued 



• Communicated by the Author. 



