Royal Astronomical Society. 311 



miocene species of Touraine agree for the greater part with species 

 now living on the western coast of France or in the Mediterranean, 

 and as the recent testacea of the crag ave identifiable with species 

 belonging to the British seas. This result appears to Mr. Lyell to 

 confirm the accuracy of conchological determinations ; for if, on the 

 contrary, it should be maintained, that the number of recent species 

 is so enormous, and different species resemble each other so closely as 

 to have produced identifications from the mere difficulty of effecting 

 discriminations, he would suggest that in that case, according to a 

 fair calculation of chances, nine-tenths of the American miocene 

 species hitherto identified ought to have been assimilated to exotic 

 shells, instead of having been found to agree with some portions of 

 the limited fauna at present known on the American shores. The 

 same argument, he adds, is clearly applicable to the identifications 

 which have been made of fossil and recent shells in the European 

 tertiary formations. 



May 18, 1842. A memoir "On the Geological Structure of the 

 Ural Mountains," by Roderick ImpeyMurchison, Esq., F.R.S., Pres. 

 G.S., Mons. E. deVerneuil, and Count A. von Keyserling, was read; 

 an abstract of which has been given in the present volume, p. 124. 



ROYAL ASTRONOMICAL SOCIETY. 

 [Continued from p. 154.] 



June 9, 1843. (Communications respecting the Comet concluded.) 

 An article by M. Capocci, on the comet, of which the following 

 is an abstract, is extracted from the Giornale della due Sicilie, of 1st 

 May, 1843, and communicated by Colonel Jackson. 



The article gives an account of a paper read by M. Capocci before 

 the Royal Academy of Sciences of Naples. M. Capocci first corrects 

 a mistake into which some observers appear to have fallen, in over- 

 estimating the length of the tail, to which some persons attributed 

 an extent of 80° to 90°, but which certainly was not visible beyond 

 40° to 45° from the nucleus. With respect to the difficulty attending 

 the orbit of the comet, he attributes it to the very small perihelion 

 distance, and the consequently very rapid angular motion at the 

 passage through the perihelion ; the comet, during the eighteen days 

 following its perihelion passage (that is, prior to the time of its first 

 observation on March 17), having gone through at least 170° of its 

 angular motion round the sun ; while, during the whole of the time 

 of its visibility afterwards, it described only 3°, from which the 

 orbit was to be determined ; whence it has happened that astrono- 

 mers of very high reputation have published results altogether false. 

 With respect to the particular difficulty attending the circumstance 

 of some of the sets of observations having given a perihelion distance 

 smaller than the sun's semi-diameter, and the apparent consequence 

 that the comet must thus either have passed within the luminous 

 matter of the sun, or have been projected obliquely from his surface, 

 M. Capocci considers that it is more seeming than real, as an error 

 sufficient to accourft for such a paradox would have excited no sur- 

 prise in an orbit with a greater perihelion distance. 



