1 58 Royal Society : — Sir D. Brewster on the Compensations 



Formation of the South-East of England." By Gideon Algernon 

 Mantell, Esq., LL.D., F.R.S. 



In this paper the author gives a description, accompanied with 

 drawings, of a remarkable fossil Turtle, referable to the genus Emys, 

 and named from its discoverer, Mr. Bensted, the Emys Benstedi, 

 which has been lately found in a quarry of the lower chalk of Kent, 

 at Burham, which is situated near the banks of the Medway, between 

 Chatham and Maidstone. The specimen discovered consists of the 

 carapace or dorsal shell, six inches in length and nearly four inches 

 in breadth, with some of the sternal plates, vertebra?, eight ribs on 

 each side of the dorsal ridge, a border of marginal plates, and one 

 of the coracoid bones. It is adherent to a block of chalk by the 

 external surface of the sternal plates. The marginal plates are 

 joined to each other by finely indented sutures, and bear the impress 

 of the horny scales or tortoise-shell, with which they were originally 

 covered. The expanded ribs are united together throughout the 

 proximal half of their length, and gradually taper to their marginal 

 extremities, which are protected by the plates of the osseous border. 

 Mr. Bell considers the species to which it belonged as being closely 

 allied in form to the common European Emys, and as possessing a 

 truly fluviatile or lacustrine character. The plates of the plastron, 

 however, as also the coracoid bone, resemble more the corresponding 

 bones of marine than of freshwater turtles. 



5. " Researches tending to prove the Non- vascularity of certain 

 Animal Tissues, and to demonstrate the peculiar uniform mode of 

 their Organization and Nutrition." By Joseph Toynbee, Esq. Com- 

 municated by Sir Benjamin Brodie, Bart., F.R.S. , &c. 



The above was only in part read. 



May 27. — The following papers were read, viz. — 



1. " On the Compensations of Polarized Light, with the descrip- 

 tion of a Polarimeter for Measuring Degrees of Polarization." By 

 Sir David Brewster, K.H., D.C.L., F.R.S., and V.P.R.S. Ed. 



In four papers published in the Philosophical Transactions for 

 1830, the author maintained, in opposition to the prevailing theory, 

 that light, either reflected or refracted at angles different from that 

 at which it is completely polarized, does not consist of two portions, 

 one completely polarized, and the other completely unpolarized, 

 but that every portion of it has the same physical property, having 

 approximated in an equal degree to the state of complete polarization. 

 This conclusion, which had been derived from reasoning on the hy- 

 pothesis that a pencil of light, composed of two pencils polarized 

 respectively at angles of -f- and — 45° with the plane of reflexion, 

 was equivalent to a pencil of common light, is confirmed in this 

 paper by experiment, made with common light itself, reflected from 

 different parts of the atmosphere, and from which the uniaxal or 

 biaxal systems of rings were obtained. On placing such a system 

 between light partially polarized in an opposite plane, the author 

 found that the rings disappeared, the direct system being seen on one 

 side of the plane of disappearance, and the complementary system 

 on the other side. In this experiment the polarization of the light 



