286 HISTORY OF ASTRONOMY. 



and seven feet square at the top, and is entirely detached 

 from the building. On the pier rests a granite block, 

 fourteen feet high, to which the great refractor is to be 

 attached. The observatory building cost $5000. 



A refracting telescope was ordered from Messrs. 

 Spencer and Eaton, of Canastota, New York, and 

 has recently been completed. The object-glass has a 

 diameter of 13 inches, with a focal length of 16 feet. 

 The hour circle, divided on silver, has a diameter of 

 15 inches, and reads by two verniers to two seconds of 

 time. The declination circle has a diameter of 26 

 inches, and reads to four seconds of arc. The filar 

 micrometer has eye-pieces made of double achromatics, 

 instead of the usual Kamsden form, giving magnifying 

 powers from 100 to 1000. The negative eye-pieces give 

 magnifying powers from 80 to 1500 times. The usual 

 sidereal motion is given by clock-work. 



The focal length of this telescope is about four feet 

 less than is usual in the Munich instruments of the same 

 aperture. The telescope is thus rendered less unwieldy, 

 and in the opinion of Mr. Spencer, its optical performance 

 is not impaired. The flint and crown discs for this 

 instrument were procured through the agents, Messrs. 

 Cook, Beckel and Co., New York, from Joseph Bader, of 

 Kohlgrub, and have been found to be remarkably exempt 

 from striaB. The object-glass has been subjected to par- 

 tial trial with very satisfactory results. The price of this 

 telescope was $10,000. The transit instrument and clock 

 have not yet been ordered. 



