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employs resembles two thimbles, fitted one within the other by 

 screwing, and with a perforation at the extremity of each. In these 

 perforations are fixed two suitable plano-convex lenses, which may 

 thus have their axes easily brought into the same line by means of 

 their plane surfaces ; while their distance from each other may be 

 adjusted by screwing, so as to produce the best effect of which they 

 are capable. The best relative proportion of the foci of the two 

 lenses, appears, from the trials made by the author, to be that of 

 three to one. The distance between their plane surfaces should, in 

 general, be about 1*4 of the shorter focus, but should be varied by 

 trial, till the utmost possible degree of distinctness has been attained. 

 The lenses must be fixed in their cells with their plane sides next to 

 the object to be viewed. The exterior cell of the compound mag- 

 nifier should be formed with a flanch, so that it may rest upon the 

 piece that receives it. The plano-convex lens, by which the object 

 is illuminated, is inclosed in a tube about six inches long, blackened 

 in the inside, and having a circular perforation below of about three 

 tenths of an inch in diameter, for limiting the lights reflected from the 

 plane mirror. The centre of this aperture must be in the common 

 axis of the lenses ; .and the image of the perforation formed by the 

 large lens, must be brought, by proper adjustment of the distance of 

 that lens, into the same plane as the object to be examined. With 

 a microscope so constructed, the author has seen the finest striae and 

 serratures upon the scales of the Lepisma and Podura, and the scales 

 upon a Gnat's wing, with a degree of delicate perspicuity not attain- 

 able with any other microscope he has tried. In consequence of the 

 plane surface of the lens being next to the object viewed, the mi- 

 croscope of Dr. Wollaston possesses the important advantage of 

 having its action undisturbed by the contact of a fluid under exami- 

 nation. 



An Account of some Experiments on the Torpedo. By Sir Humphry 

 Davy, Bart. F.R.S. Read November 20, 1828. [PAzV. Trans. 1829, 

 p. 15.] 



The author, after noticing the peculiarities discovered by Walsh 

 in the electricity of the Torpedo, and the opinion of Cavendish, that 

 it resembles the action of an electrical battery weakly charged, ad- 

 verts to the conjecture of Volta, who considered it as similar to that 

 of the galvanic pile. Being on the coast of the Mediterranean in 

 1814 and 1815, the author, desirous of ascertaining the justness of 

 Volta's comparison, passed the shocks given by living torpedos 

 through the interrupted circuit made by silver wire through water, 

 but could not perceive the slightest decomposition of that fluid ; the 

 same shocks made to pass through a fine silver wire, less than one 

 thousandth of an inch in diameter, did not produce ignition. Volta, 

 to whom the author communicated the results of these experiments, 

 considered the conditions of the organs of the torpedo to be best re- 

 presented by a pile, of which the fluid substance was a very imper- 



