400 SEC. 11. ASTRONOMY. 



1784b. Gregorian Telescope, made by the celebrated 

 John Hadley, A.D. 1726, and handed down in his family as being 

 the first telescope of the kind ever made. 



Cambridge Observatory, J. C. Adams, Director. 



1787. Small Universal Equatorial, formerly belonging to 



the late Dr. W. H. Wolla-ston. //. Wollaston Blake. F.R.S. 



1785. Eight and a half inch Reflecting Telescope, with 

 parabolised silvered glass mirror. John Browning. 



Equatorially mounted, with powerful driving clock, battery of improved 

 achromatic eye-pieces, double prism solar eye-piece for observations of the Sun, 

 Position micrometer, and new double image micrometer, with rotating hour 

 circle, to facilitate finding objects without calculations. 



1786. Four and a half inch Reflecting Telescope, with 

 parabolised silvered glass mirror, on parallactic stand, for following 

 the heavenly bodies with a single motion. John Browning. 



This instrument was contrived for educational purposes ; the mirrors are 

 warranted to be of such quality as to bear well a power of 500 diameters. 



1788. Equatorial, small, capable of carrying a telescope of 

 3 to 3 1 inch aperture with perfect steadiness. Yeates $ Sons. 



1789. Photograph of Equatorial Mounting of a Re- 

 fractor, of 9" aperture and 13' focal length, with micrometer and 

 position-circle at the eyepiece. A. Rcpsold and Sons, Hamburg. 



The declination circle can be read close to the eyepiece of the telescope ; 

 it is illuminated by the lamp which illuminates the cross-wires in the field 

 of view of the telescope. By means of one perpendicular roller beneath the 

 centre of gravity, the pressure of the hour axis on the bearings is removed. 

 The clockwork is arranged in the head of the cast-iron column of which the 

 foot is below the floor. 



1790. Orbit-sweeper. Equatorial arrangement of a telescope 

 of 6" aperture, 8' focal length, with third axis, 1874. Constructed 

 for the Observatory of Strassburg. (Photograph.) 



A. Repsold and Sons, Hamburg. 



In this equatorial arrangement the head of the declination axis carrries 

 at right angles the socket of a third axis, about which the telescope can be 

 revolved, whilst its optic axis is inclined to the third axis at an angle of 

 90 + 2. By means of this arrangement a quickly moving celestial body 

 can be easier found, as the third axis is directed to the pole of the projection 

 of its orbit. (See G. B. Airy's observations on an " Orbit-sweeper," in the 

 monthly notices of the E. Astron. Soc.) The telescope can also be placed 

 parallel to the third axis at the head of the declination axis, and has then 

 only an equatorial movement. This instrument is provided with clockwork, 

 and has a changeable polar distance from to 66. 



1791. Model of the Great Melbourne Reflector, com- 

 pleted by Messrs. Grubb & Son in 1868. Scale, f inch to a 

 foot ( T V). Howard Grubb, F.R.A.S. 



