ISM.] Philosophical Transactions, Part I. 1814. 447 



constant quantity. Dr. Brewster found the constant quantity for 

 crown glass to be 41 '84. If we divide this constant quantity by the 

 number of plates, the quotient will be the natural tangent of the 

 angle at which that number will polarize a pencil of light. This 

 law has enabled the author to construct a table exhibiting the angles 

 of incidence at which a ray of light is polarized by any number 

 of plates from one to 8,610.000. 



Dr. Brewster likewise observed, as Mai us had done before him, 

 that the ray of light was polarized by transmission in the opposite 

 way from what it was by reflection, and that the whole of the trans- 

 mitted light being polarized will pass through the glass plates with- 

 out any of it being lost. 



13. Farther Experiments on the Light of the Cassegrainian 

 Telescope i am pared with that of the Gregorian. By Captain Henry 

 Kater, Brigade Major. — In this paper Captain Kater relates another 

 experiment which he made on the relative intensity of the light of 

 these two telescopes. It confirmed his preceding results. It seems 

 to follow from these experiments that the light of the Cassegrainian 

 telescope is to that of the Gregorian as 234 to 100. In an appendix 

 to the paper Capt. Kater relates a number of experiments made to 

 determine the relative intensity of light from a concave mirror at 

 equal distances from the focus within and without. From these 

 experiments it would appear that the intensity of the light within 

 the focus is to that without very nearly in the ratio of two to one. 

 The mean of all the experiments give the ratio 1000 to 503*68. 



14. Astronomical Observations relating to the Siderial Part of the 

 Heavens, and its Connection with the Nebulous Part, arranged for 

 the Purpose of' a Critical Examination. By William Herschel, 

 LL. D. F. R. S. — Dr. Herschel, with whose ingenuity and origina- 

 lity of ideas most of our readers are sufficiently acquainted, has 

 been occupied for many years in studying the structure of* the 

 siderial heavens. He has at last started an opinion respecting the 

 formation of the stars, which he has supported in several papers 

 with much skill and address. The numerous nebulosities which 

 fill the heavens, being gradually condensed by gravitation, are con- 

 verted into stars. Stars ready formed occasionally attract nebulosi- 

 ties, and increase in size. "Neighbouring stars by mutual attraction 

 gradually approach other, and constitute globular clusters. Such is 

 a short outline of the hypothesis. The present paper consists in a 

 kind of arrangement of facts in support of the probability of the 

 hypothesis. It is not very susceptible of abridgment, and indeed 

 requires the knowledge of several of Dr. Herschel's previous papers 

 to be completely understood. These reasons prevent me from 

 attempting to lay a view of it before the reader. There is another 

 reason also which has some weight with me. I consider it as 

 treating of a subject beyond the reach of our limited means of 

 investigation upon this earth ; and as the objects of investigation 

 which find a place in the /1/ir/a/-, of Philosophy are of B very diffe- 

 rent kind, I conceive the present paper to he in some measure 

 beyond our province. 



