Miscellanies. 187 



Mechanic Arts, to whom was referred for examination a Reflecting 

 Telescope, made by Mr. Amasa Holcomb, of Southwick, Hampden 

 County, Massachusetts : Report — 



That the following description of the instrument is given by Mr. 

 Holcomb. " The telescope is of the reflecting kind, and has a focnl 

 length of six feet. The diameter of the specwlum 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 astro- 

 nomical 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 Herschel ; the ob- 

 server having his back towards the object, and looking directly to- 

 wards the speculum. It has the advantage over those of the Grego- 

 rian 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 proportion to the length of the 

 instrument. It will bear a diameter of eight inches with much ad- 

 vantage, for viewing very small stars, in consequence of the great in- 

 crease of light. The magnifying powers used are forty, ninety and 

 two hundred and fifty." 



Through the politeness of Prof. Alexander Dallas Bache, the 

 committee were permitted to compare the performance of Mr. Hol- 

 comb's reflector with that of a five feet achromatic of four inches ap- 

 erture, by Dollond, the property of the University of Pennsylvania. 

 The instrument was also compared with a three and a half feet ach- 

 romatic by Dollond, and with a Gregorian of four inches aperture, 

 the mirrors of which had been lately repolished in London. The 

 short stay of Mr. Holcomb in Philadelphia, prevented the compari- 

 son 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 ad- 

 journment in the open lot south of the Pennsylvania Hospital, the 

 use of which was politely permitted to the committee by the mana- 

 gers of that institution. The following were the results of the com- 

 parison : — The moon, nearly full, was too bright to be viewed with 

 the lower powers of the instruments ; with the power of 350 in the 

 five feet achromatic, the moon appeared bright and well defined ; — 

 with the same eye piece, giving a power of 400, in the reflector by 

 Mr. Holcomb, the moon was sufficiently bright, and equally well de- 

 fined. The same (with the exception that the moon was more bril- 



