Appendix 



Reports of Committees 

 OF THE Franklin Institute 



[From Journal of the Franklin Institute, July 1834, new ser. 

 vol. 14 (whole no. 18), pp. 169-172.] 



Report on Amasa Holcomb' s Ke fleeting Telescope. 



The Committee on Science and the Arts, constituted by the 

 Franklin Institute of the State of Pennsylvania for the pro- 

 motion of the Mechanic Arts, to whom was referred for 

 examination a Reflecting Telescope, manufactured by 

 Mr Amasa Holcomb, of Southwick, Hampden county, Mas- 

 sachusetts, 



REPORT:— 



That the following is the description of the instru- 

 ment as given by Mr. Holcomb. 



"The telescope submitted to the examination of the Com- 

 mittee of the Franklin Institute is of the reflecting kind; has 

 a focal length of six feet; the diameter of the speculum is 

 three inches nine-tenths; the rays of light are reflected but 

 once; the image formed in the focus of the speculum is 

 viewed by a common astronomical eye piece, or by a single 

 lens; it has also an eye piece for viewing land objects, which 

 shows them erect. The telescope is of the same construction 

 as those of Sir William Herschell, the observer having his 

 back towards the object and looking direcdy towards the 

 speculum. It has an advantage over those of the Gregorian 

 and Newtonian forms, by showing the object brighter with 

 the same aperture, there being no light lost by a second 

 reflection. The diameter of the speculum is small in pro- 

 portion to the length of the instrument; it will bear a di- 

 ameter of eight inches, with much advantage for viewing 

 very small stars, in consequence of the great increase of 

 the light. 



The magnifying powers that are used are, forty, ninety, 

 and two hundred and fifty." 



Through the politeness of Prof. A. D. Bache, the 

 committee were permitted to compare the perfor- 

 mance of Mr. Holcomb's reflector with that of a 

 five feet achromatic, of four inches aperture, by 

 DoUand, the property of the University of Pennsyl- 

 vania. The instrument was also compared with a 

 three and a half feet achromatic, by Dolland, and 

 with a Gregorian of four inches aperture, tne mirrors 

 of which had been lately repolished in London. 



The short stay of Mr. Holcomb in Philadelphia, 

 prevented the comparison of it with reflectors in the 

 possession of other members of the committee. 



On the evening of the 14th of April, the committee 

 met by adjournment in the open lot south of the 

 Pennsylvania Hospital, the use of which was politely 

 permitted to the committee by the managers of 

 that institution. 



The following were the results of the comparisons: — 



The moon, nearly full, was at a height to be con- 

 veniently viewed with the lower powers of the in- 

 struments: with a power of 350 in the five feet 

 achromatic, the moon appeared bright and well 

 defined, — with the same eye-piece, giving a powei 

 of 400, in the reflector by Mr. Holcomb, the moon 

 was sufficiently bright, and equally well defined. 

 The same, with the exception that the moon was 

 more brilliant, and the field of view much greater, 

 was remarked with the use of Mr. Holcomb's highest 

 magnifier, giving a power of two hundred and fifty. 



As an illustration of their comparative performances, 

 it was remarked that the waved appearance of the 

 outer declivities of the craters of some of the apparently 

 extinct lunar volcanoes, indicating the successive 

 depositions of the lava, was more ro.anLfest with a 

 power of four hundred in the reflector. 



The immersions of 3 and 4 Geminorum of the 

 sixth and seventh magnitude, were observed at the 

 same instant of time in each. 



The same occurred the evening before with a star 

 of the eighth or ninth magnitude. 



The immersions, however, of two very small stars, 

 apparently of the tenth or eleventh magnitude, were 

 observed with difficulty in the refractor, but could 

 not be observed at all in the reflector. 



The comparison of Polaris was best seen when 

 the moon was up in the refractor, but in the absence 

 of the moon it was readily seen in both. 



Castor was easily divided with the lower powers of 

 either, but in the case of this, as well as of other 

 binary and double stars, the dark space between the 

 stars was less disturbed by scattering rays in the 

 reflector than in the refractor. 



e Bootes was seen double in each, but more dis- 

 tinctly in the reflector, fi Draconis, 7 Leonis, and 4th 

 and 5th e Lyra, were seen distinctly double in both 



PAPER 26: THREE 19TH-CENTURY AMERICAN TELESCOPE MAKERS 



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