1868.] Report of the Committee on the Melbourne Telescope. 313 



April 2, 1868. 

 Lieut.-General SABINE, President, in the Chair. 

 The following communication was read :— - 



Report of the Committee on the Melbourne Telescope to the Presi- 

 dent and Council of the Royal Society.^^ Communicated by the 

 President. 



The Committee were informed by Mr. Grubb at the close of last year that 

 the telescope was ready for their final examination ; but the bad weather 

 which has prevailed in Ireland ever since precluded all trials of its optical 

 power till February 17, when they met at Mr. Grubb' s works in Rath- 

 mines Road. 



1 . The telescope was not finished at the time named in the contract ; but 

 the Committee have ascertained that the delay arose solely from un- 

 favourable weather, which not only impeded the actual work of polishing, 

 but for weeks together made it impossible to test the figure of the specula. 

 They considered that it was far m^ore important to send out a perfect 

 instrument than to keep the exact time. 



2. The Committee, after minutely and carefully studying the mechanical 

 details of the equatorial, have come unanimously to the conclusion that it 

 is a masterpiece of engineering. Its movements are surprisingly smooth 

 and steady ; it can be moved to any portion of the sky, even if it have to 

 be reversed from one side of its pier to the other, in less than a minute by 

 two operators and with very little exertion. 



The clock is smooth and equable in its action, it is very powerful, and 

 quite equal to its work. Great change of rate, as from sidereal to lunar 

 time, is effected by an ingenious piece of differential gearing ; small changes 

 are made by a cam adjustment ; moreover it rings seconds, for the double 

 object of comparing its rate with a chronometer and to assist the observer 

 in his observations. 



3. The Committee are strongly impressed by the great convenience to 

 the observer of the arrangements of the hour and polar-distance circles, the 

 facility of controlling their adjustment, and the easy access to the eyepiece. 



4. The stabiUty of the tube was severely tested, both in respect of its 

 general stiffness and its power of resisting torsion, such as might be pro- 

 duced by the weight of the small speculum when the telescope is off the 

 meridian ; and the results were highly satisfactory. 



5. In large reflecting telescopes it is usual to make provision for keeping 

 a given diameter of the great speculum always in a vertical plane. When 

 they are equatorially mounted, this is done by rotating the tube in its 

 cradle. Here the tube does not turn ; but there is a special arrangement 

 of hoop-suspension, by which, whatever diameter may be vertical, it is 

 supported in a uniform and symmetrical manner. The system of trian- 



VOL. XYI. 2 G 



