420 SEC. 11. ASTRONOMY. 



graduated divisions, and on the inner the hours of the day. In the inner 

 slide there is a small hole which must be made to correspond to the month in 

 which it is used. The circle is held up to the sun, the inner surface is then 

 in shade and the sunbeam shining through the little orifice forming a point 

 of light upon the hour marked on the inner side. In Knight's pictorial 

 edition of Shakspere, "As you like it," p. 231, is a representation of a similar 

 instrument. 



The slide with the hole was wanting when it was brought to the exhibitor 

 and was added by him, and the drawings of the whole were made by Mr. 

 William Knight of Petworth. 



1849b. Dial of a later date and more complicated construction. 



John Ayling Blag din. 



The same rules as above apply to this instrument, which was given to the 

 exhibitor's father about 45 years ago by the Rev. Deival of Duncton. 



1849c. Brass Instrument, apparently used as a Sun 

 Dial. Maker, Sauter, Petersburg. W. Clinton Baker. 



VI. SIDEROSTATS. 



1851. 's&ravesande's Heliostat, with his Equatorial 

 Clock. Conservatoire des Arts et Metiers, Paris. 



185 la. Siderostat, by Foucault. Paris Observatory. 



185 Ib. Heliostat, by Gamberg. Paris Observatory. 



1851c. Heliostat, by Silbermann. M. J. Duboscq, Paris. 



185 Id. Heliostat, by Foucault. M. J. Duboscq, Paris. 



185O. Universal Heliostat, designed by Col. Campbell, and 

 executed by Adam Hilger, 192, Tottenham Court Road. 



Lieut.- Colonel Archibald C. Campbell. 



This instrument, after the polar axis has been set due north and south, and 

 adjusted for latitude, will throw the light of a star or the sun in any required 

 direction, and will keep it there by means of the clock ; all the slow motions 

 in altitude and azimuth can be manipulated by the observer without 

 stopping the instrument. The connexions are placed ready to the observer's 

 hand, wherever he may be. 



A small telescope is also attached to the polar axis, so that it may act rs a 

 finder for any object, which, when seen in this telescope, will be reflected 

 by the mirror to the required spot. The mirror is 1 foot by 8 inches, and is 

 a perfect plane. This was also constructed by Mr. Hilger. 



Dimensions. Iron stands, 30 ins. diameter ; height, 3 ft. 2 in. to centre of 

 mirror. Mirror, 1 ft. by 8 in. 



185 le. Photograph of a Siderostat, constructed by 

 Messrs. Cooke and Sons of York, for the Royal Society. 



J. Norman Lockyer, F.R.S. 



