389 



dispersive powers, accordingly, the unpolarized light which remains 

 in the extraordinary image must be coloured at all incidences, the 

 colours being most distinct near the maximum polarizing angle. 

 This necessary result of the formula, the author finds to be experi- 

 mentally true in oil of cassia, and various highly dispersive bodies ; 

 hence there can be no angle of complete polarization for white light. 



The same law which determines the polarization of light by re- 

 flexion is applicable also to that by refraction ; in both cases, the 

 analysing doubly-refracting crystal is insufficient to distinguish light 

 completely polarized from light in a state of approach to polarization. 

 The difference, however, between these two kinds of light, is marked 

 by most distinctive characters, and shows itself in some of the most 

 complex phenomena of interference. Hence the author is led to 

 consider common light as composed of rays in ever} 7 state of positive 

 and negative polarization, or of particles having planes, which are 

 acted upon by the attractive and repulsive forces residing in solid 

 bodies ; such planes having every possible variety of inclination to a 

 plane passing through the direction of their motion. The formulae 

 given in the paper represent the laws according to which the re- 

 pulsive and attractive forces change the position of the planes of po- 

 larization ; so that the author regards all the various phenomena of 

 the polarization of light by reflexion and refraction, as now brought 

 under the dominion of laws as well determined as those which regu- 

 late the motions of the planets. 



A Report on the Stomach of the Zariffa. By Sir Everard Home, Bart. 

 V.P.R.S. Read December 24, 1829. [Phil. Trans. 1 830, p. 85.] 



In common with other ruminant quadrupeds, the Zariffa has a 

 stomach consisting of four cavities. The efflorescence which lines 

 the paunch is similar to that of the bullock, but is more prominent ; 

 the second cavity is destitute of the cellular structure met with in 

 other ruminants, but the third and fourth cavities exhibit no peculi- 

 arities ; the cud formed from the leaves and twigs of the acacia, 

 which are the natural food of the Zariffa, is so succulent, as not to 

 require being again moistened in passing through the second sto- 

 mach, as is the case with grass ; this cavity is therefore not furnished 

 with the cells which are provided for this purpose in herbivorous 

 quadrupeds. 



Three drawings of the structure of the parts described accompany 

 the paper. 



On the Production of regular double Refraction in the Molecules of 

 Bodies by simple Pressure ; with Observations on the Origin of the 

 doubly refracting Structure. By David Brewster, LL.D. F.R.S. 

 L. # E. Read February 11, 1830. [Phil. Trans. 1830, p. 87.] 



The author has already shown, in former papers which have ap- 

 peared in the Philosophical Transactions, that the phenomena of 



