514 



The nebulae, of which an account is given in this paper, were ob- 

 served with the speculum of three feet aperture described in the 

 Philosophical Transactions for 1840 : and the object of the observa- 

 tions was rather to test its powers and to decide the merits of pro- 

 gressive experiments than to seek for astronomical results. Sketches 

 are given of the actual appearance of five of the nebulae observed, 

 namely those numbered 88, 81, 26, 29 and 47 in Sir John Herschel's 

 catalogue. The author observes, in conclusion, that all that he has 

 seen confirms the accuracy of Sir John Herschel's judgment in 

 selecting the nebulae which he places in the class designated as re- 

 solvable ; and that every increase of instrumental power still con- 

 tinues to add to the number of the clusters at the expense of the 

 nebulae, properly so called. It would still, however, be unsafe, he 

 further remarks, to conclude, that such will always be the case, and 

 thence to draw the obvious inference that all nebulosity is but the 

 glare of stars too remote to be separated by the utmost power of 

 our instruments. 



June 20, 1844. 

 JAMES WALKER, Esq., V.P., in the Chair. 



1. " On the Structure of the Ultimate Fibril of the Muscle of 

 Animal Life." By Erasmus Wilson, Esq., Lecturer on Anatomy 

 and Physiology in the Middlesex Hospital; in a Letter addressed 

 to Peter Mark Roget, M.D., Sec. R.S. Communicated by Dr, 

 Roget. 



By resorting to peculiar methods of manipulation, and employing 

 a microscope of more than ordinary power, the author, with the 

 assistance of Mr. Lealand, has succeeded in discovering the real 

 structure of the ultimate muscular fibril, in a specimen taken from 

 the arm of a strong healthy man immediately after its amputation. 

 Pie finds each fibril to be composed of minute cells, disposed in a 

 linear series, flattened at their surfaces of apposition, and so com- 

 pressed in the longitudinal direction as to leave no marginal in- 

 dentation on the surface ; thus constituting a uniform cylinder, 

 divided into minute subdivisions by transverse septa, which are 

 formed by the adherent surfaces of contiguous cells. The diameter 

 of the fibril, in the state of relaxation, is the 20,000th part of an 

 inch. The cells are filled with a transparent substance, to which 

 the author gives the name of Myoliiie, and which differs in its re- 

 fractive density in different cells. In four consecutive cells the 

 myoline is of greater density than in the four succeeding cells, and 

 this alternation is repeated throughout the whole course of the fibril. 

 In consequence of all the fibrils composing the ultimate fasciculus 

 having the same structure, and the cells, which are in lateral juxta- 

 position, containing myoline of the same density, they act similarly 

 on light, and the whole presents, to the eye of the microscopic ob- 

 server, a succession of striae or bands, dark and luminous alternately, 

 and transverse to the direction of the fasciculus ; an appearance 



