Aslronomicdl Society, 291 



I have quoted these remarkable passages at length, because 

 it appears to me that what is there advanced merely as a hy- 

 pothesis, acquires a considerable degree of probability from 

 the facts which I have stated, since I have succeeded in ren- 

 dering actually visible circular particles of excessive minute- 

 ness, in each of which die microscope detects the very struc- 

 ture imagined by Brewster, viz. the black cross and four sec- 

 tors of light. So that it appears not improbable tliat the cir- 

 cular-polarizing properties of fluids may be owing to the pre- 

 sence of multitudes of particles similar to these, which they 

 hold in solution. 



L X I . Proceedtfigs of Learned Societies. 



nOYAL ASTRONOMICAL SOCIETY. 



Nov. 13, 'T^HE following communications were read: — 

 J 835. -•- 



I. Two elementary solutions of Kepler's Problem, by the angular 

 Calculus. By VV^illiam Wallace, A.M., &c. &c.. Professor of Mathe- 

 matics in the University of Edinburgh. 



II. Observations of Mars at the opposition 1834-35, made at the 

 Observatory, Cape of Good Hope. By Mr. Maclear. 



These observations, which, including the stars observed with 

 the planet, are nearly 20l) in number, were made between Novem- 

 ber 23, 1834, and February 10, 1835. They are entirely made with 

 the mural circle, and appear to have been forwarded immediatelv 

 to England. 



III. Letter from Mr. Snow to the Secretary, dated October 9, 

 1835, on the latitude of his observatory at Ashurst. 



The method here adopted by Mr. Snow was invented by the 

 celebrated Romer, above 130 years ago, but has ever since remained 

 unnoticed, till within these few years, when it has been used in the 

 determination of the latitudes of places, in some geodesical measure- 

 ments on the Continent. The method is described by Bessel, in Schu- 

 macher's Astroyiomische Nachrichten, a translation of which is given in 

 the Philosophical Magazine for May, 1825 (First Series, vol. l.xv. 

 p. 354.) J and it is also noticed by Dr. Pearson, in his Astronomy, vol. ii. 

 p. 594. If the declination of the star can be relied on, the method is 

 capable of great accuracy: the mode pursued was as follows. — A transit 

 instrument was placed with its axis north and south, so that the 

 eastern and western passages of a star over the prime vertical might 

 be observed, and the latitude might then be deduced from the known 

 declination of the star. The assumed declinations were taken from 

 Pond's catalogue of 1112 stars ; the instrument was kept carefully 

 adjusted for level, and the error of coUimation, known to be small, 

 was eliminated by reversing the telescope on different evenings. 

 The transit telescope was of twenty inches focal length, and the 



2L2 



