Miscellanies. 189 



titude, though quite constrained and inconvenient in using the achro- 

 matic. 



The reflector gave a distinct view of land objects even when with- 

 in one fourth of a mile : some light was lost by the position of the 

 head, an inconvenience partially obviated by making the end nearest 

 the object three inches greater in aperture. 



The Gregorian, which was probably not a very fine instrument of 

 its kind, bore no comparison in distinctness, or in quantity of light 

 with the Herschelian telescope. 



From these trials the committee are of opinion, that Mr. Holcomb 

 has been entirely successful in the difficult art of polishing specula 

 with the true curve, which gives to the object viewed all the distinct- 

 ness of figure that is given them by the best refractors by Dollond. 



In one respect, the largeness of the field of view, the reflectors by 

 Mr. Holcomb have a decided advantage over achromatics and re- 

 flectors of different construction : the apparent diameter of the 

 field of view in the Herschelian, being nearly double that of either, 

 with equal freedom from aberration. 



The quantity of light furnished by the refractor was greater with 

 the same aperture ; an important advantage in searching for, and ob- 

 serving, very minute objects. This deficiency of light, in the Her- 

 schelian, for viewing faint objects near the moon, or satellites near 

 their primaries, the committee are of opinion may be removed by en- 

 larging the aperture of the Herschelian reflector to five or five and a 

 half inches. 



The simplicity of the method of preparing and mounting Mr. 

 Holcomb's telescope is worthy of notice, since on this plan the artist 

 is enabled to furnish for an expense of one hundred dollars, with 

 plain mounting, or of one hundred and fifty to two hundred dollars, 

 with more expensive mounting, telescopes whose performance equals 

 that of Gregorian and achromatics, hitherto imported into the country 

 at an expense of five hundred dollars. 



(A true copy by order of the committee,) 



William Hamilton, Actuary, 



Philadelphia, May 8th, 1834. 



Extracted and Translated by J. Chiseom. 



23. On Electromotors. — The Abbe S. Dal Negro, Professor of 

 Physics at Padua, having ascertained by multiplied experiments 

 that the smallest plates of zinc produced the greatest relative efl'ect, 



