453 



from milk than the cardiac portion of the stomach. The cardiac 

 portion of the stomach of the hawk was found more powerful than 

 the same part of a common fowl. 



The gastric glands were carefully dissected out from behind the 

 membrane that lines the cardiac extremity of the stomach of a turkey ; 

 and of these, forty grains, by weight, were taken, and their effect 

 compared with an equal weight of membranous lining of the same 

 cavity, an equal weight of membrane from the fourth cavity of a calf's 

 stomach in a recent state, and forty grains of dry rennet. Since the 

 last must have been prepared from about four times its weight of re- 

 cent membrane, its effect was produced in much the shortest time. 

 The coagulation effected by the gastric glands took place nearly at 

 the same time as by the recent calf's stomach; while that from the 

 lining of the turkey's stomach was nearly three times as long in pro- 

 ducing the corresponding effects. 



From these experiments, the author infers that the secretion from 

 the gastric glands possesses the power of coagulating milk, and com- 

 municates that property to adjacent parts, by which it is imbibed. 



On some Properties of Light. By David Brewster, LL.D.F.R.S.Edin. 

 In a Letter to Sir Humphry Davy, LL.D. F.R.S. Read January 

 28, 1813. [Phil. Trans. 1813, p. 101.] 



The author, having been for some time past engaged in a course 

 of experiments on the refractive and dispersive powers of different 

 substances, the details of which are intended for future publication 

 in a separate work, confines himself, at present, to a relation of such 

 of his results as have most of novelty or importance. After repeating 

 the experiments that have been made by others on the properties 

 that light acquires by transmission through Iceland-spar, and upon 

 the corresponding properties of reflected light originally discovered 

 by Malus, and by him termed polarization, Dr. Brewster observed a 

 singular appearance of colour on each side of a luminous object, 

 viewed through a thin slice of laminated agate. Upon examination 

 of these coloured images through a prism of Iceland-spar, this light 

 was found to be similarly polarized, so as to appear or disappear ac- 

 cordingly as the laminae of the agate were parallel or transverse to 

 the principal section of the spar. He found also that the colourless 

 light transmitted directly through the agate, and from which the 

 coloured rays had been separated, was polarized as well as the co- 

 loured rays, appearing and disappearing alternately with them during 

 the revolution of the spar. And accordingly when light previously 

 polarized by reflection was received upon the agate, its transmission 

 or reflection depended on the relative position of the laminae of the 

 agate to the plane of reflection ; for when these were at right angles 

 to each other, no light whatever was transmitted. 



In the same manner light polarized by transmission through the 

 laminated agate, manifested the usual properties of light so affected 

 by other means. 



