BIBLIOGRArHY OF IIEKSCIIEL's WRITINGS. 557 



Ilerschel W.: Synopsis of the Writin-gs of— Contiuued. 



A. D. Vol. P. 



1795 85 378 Tiuder and setting quadrant. 



380 I liavc in 1789 many times taken up Saturn two or three hours hefore 

 its meridian passage and kept it in view with the greatest facility 

 till two or three hours aftc^r the passage, with a single assistant. 

 382 The method of observing is by what I have called the front view. 



382 The observing chair is fastened to the instrument. 



383 The aperture of the telescope is 4 feet. 



384 In making sweeps several conveniences are reciuired [as given]. 



385 A speaking pipe was led from the observer to the recorder, etc. 

 387 Right ascension apparatus. 



390 Polar distance machine : the sidereal clock by Siikltox. 



390 Polar distance piece [described]. 



396 In 1783, when I began my sweeps, no catalogue of stars in zones ex- 

 isted. I therefore gave a pattern to my indefaiigable assistant, 

 Carolina Herschel, who brought all the British catalogue into 

 zones of 1° each from 45 N. P. D. to the horizon, and put the right 

 ascensions in time. This catalogue was afterwards completed to 

 the pole in zones of .5°. 



398 A zone clock described. 



403 The construction of the great mirror is as in fig. 4(). The metal is 49^ 



inches in diameter ; 48 inches are polished. Its thickness, which is 

 equal throughout, is 3i inches ; its weight when cast was 2,118 lbs. 



404 It is swung in a ring. 



406 The surface is protected from damp by a tin cover. 

 409 Method of mounting the eye-pieces. \Vm. Herschel. 



[Dated] Slough, near Windsor, May IS, 1795. 

 Plates. 

 408 Plate XXIV: General View: "To George the Third, King of Great 

 Britain &c. This View of a Forty- Foot Telescope constructed 

 under his Royal Patronage, is with permission, most humbly in- 

 scribed, by his Majesty's very devoted and Loyal Subject, and most 

 grateful obedient Servant, William Herschel." 

 1796 86 133 Additional oUervafiom on the Comet. [1796, I.] By William Her- 

 schel, LL. D., F. R. S. [Read November 12, 179o.] 

 1796 86 166 On the method of ohm-ving the changes that happen to the fixed stars ; ^ci^h 

 some remarks on the stahiliti, of the Light of our Sun. To which ts added 

 a Catalogue of Comparative Brightness for ascertaining the Permanency 

 of tlie Lustre oj Stars. By William Herschel, LL. D., F. R. S. Read 

 February 25, 1796. 

 166 The earliest observers noted the ditTerent brilliancy of stars and have 

 classed them into magnitudes. Brightness and [apparent] size 

 were taken as synonymous terms, atul may still be used as such, 

 notwithstanding the latter must be a consequence of the former. 

 166 If we suppose the stars to be about the size of our sun and at nearly 

 an eqiial distance from ns and from each other, those which form 

 the first enclosure about us will appear brighter than the rest, and 

 there can only be a small number of them. 



166 This hypothesis is nearly confirmed by observation, as may be seen 



by looking over a globe and applying a pair of compasses op. ned 

 to 60^. Eleven pairs of 1st mag. stars are about 60° apart. 



167 Eight other pairs are near enough to 60^ to support this hypothesis. 



4h 



