ASTRONOMICAL OBSERVATORIES. 249 



The " Grand Kefractor" was made by Messrs. Merz 

 and Mahler, of Munich, Bavaria. . They bound them- 

 selves by contract to make two object-glasses of the clear 

 aperture of 15 inches, to be at least equal to that fur- 

 nished for the noble instrument now mounted at the 

 Eussian observatory at Pulkova. Oil being notified of 

 the completion of these object-glasses, the agent of the 

 University, Mr. Cranch, of London, accompanied by the 

 instrument-maker, Mr. Simms, proceeded to Munich, and 

 after careful trial and examination, made the required 

 selection. The selected object-glass was received at 

 Cambridge in December, 1846; the great tube and its 

 equatorial mounting did not arrive until June, 1847. The 

 object-glass of the telescope is 15 inches in diameter, 

 and has 22 feet 6 inches focal length. Some of the 

 eye-pieces are 6 inches long, making the entire length 23 

 feet. The telescope has eighteen different powers, rang- 

 ing from 103 to 2000. The hour circle is 18 inches in 

 diameter, divided on silver, and reading by two verniers 

 to one second of time. The declination circle is 26 

 inches in diameter, divided on silver, and reads by four 

 verniers to four seconds of arc. The movable portion 

 of the telescope and machinery is estimated to weigh 

 about three tons. It is, however, so well counterpoised 

 in every position of the telescope, and the effects of 

 friction are so far obviated by an ingenious arrangement 

 of rollers and balance-weights, that the observer can 

 direct the instrument to any part of the heavens by a 

 slight pressure of the hand upon the ends of the balance 



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