l** Royal Societj/. 



the author states that in order to obtain a clear and well-defined 

 image of an^^ object on the Daguerreotype plate, he generally found 

 it necessary to adjust the focus on the ground glass by another ob- 

 ject brought considerably nearer to the camera than the object 

 whose picture was required. When this adjustment is made, he 

 proceeds to apply the principle practically to the taking of portraits. 

 He finds that in achromatic object-glasses the focus of photogenic 

 action is not coincident with the visual focus ; and the distance be- 

 tween these two foci varies according to the nature of the combina- 

 tion of the glasses, to their different dispersive powers, and to the 

 degree of intensity of the light. By attention to these circumstances 

 in accurately adjusting the DagueiTeotype plate to the situation of 

 the focus of the photogenic rays, the author has succeeded in ob- 

 taining the most perfect delineations of objects*. 



4. " Observations on some of the Nebulae." By the Earl of Rosse, 

 F.R.S. 



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 Herschers 

 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 f. 



June 20.— 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. 

 He 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 



* The necessity of the adjustment here alluded to was first pointed out 

 by Mr. Towson, in 1839. See Phil. Mag. S. 3. vol. xv. p. 381. --Edit. 

 t See Phil. Mag. S. 3. vol. xix. p. 588.— Edit. 



