506 



other ; and he takes care to mention such other precautions as may 

 not immediately occur to artists in the employment of a new appa- 

 ratus, and to delineate accurately all those parts which might not be 

 thoroughly understood by a mere verbal description. 



Results of some recent Experiments on the Properties impressed upon 

 Light by the Action of Glass raised to different Temperatures, and 

 cooled under different Circumstances. By David Brewster, LL.D. 

 F.R.S. Edin. and F. A.S.Ed, in a Letter to the Right Hon. Sir Joseph 

 Banks, Bart. K.B. P.R.S. Read May 19, 4814. \Phil. Trans. 

 1814, p. 436.] 



The author, being engaged in making a variety of experiments on 

 resinous and other bodies that could be fused between plates of glass, 

 remarked a partial depolarization while the subject of examination 

 was hot, but which diminished on cooling, and consequently could 

 not be ascribed to incipient crystallization. He therefore tried a plate 

 of glass alone ; and having previously raised its temperature almost 

 to a red heat, he found that a ray of polarized light became com- 

 pletely depolarized by its passage through it : and he further thence 

 infers, that glass brought to a certain temperature forms two images, 

 and polarizes them like all doubly refracting crystals, only that the 

 two images are, in fact, coincident, instead of being separated. 



Since in the formation of the glass-tears, called Prince Rupert's 

 drops, which are made by dropping melted glass into cold water, it 

 is probable that in consequence of the sudden consolidation at the 

 surface, the interior part is prevented from contracting, and conse- 

 quently retains, in some measure, that relative distance of its particles 

 which obtained in the fluid state, the author conceived these drops 

 to be a fit subject for an interesting experiment ; and having pro- 

 cured several such drops, made of white flint-glass, he cut and po- 

 lished one of them by two planes at right angles to the axis, and a 

 second by two planes parallel to its axis and to each other. When 

 polarized light was transmitted through a drop in either of these di- 

 rections, it was found to be depolarized ; but there was not any po- 

 sition in which the transmitted ray would retain its polarization, as 

 is found in corresponding experiments with crystallized substances. 



Consideration of various Points of Analysis. By John F. W. Herschel, 

 Esq. F.R.S. Read May 19, 1814. [Phil. Trans. 1814, p. 440.] 



This paper is divided into four sections, the first of which treats 

 of the calculus of generative functions, and relates solely to charac- 

 teristic notation, and to the method of separating the symbols of 

 operation from those of quantity. The second relates to logarithmic 

 transcendants, with a variety of remarkable results deduced from 

 them. The third relates to functional equations. The fourth to dif- 

 ferential equations of the first degree. But the whole of this paper 

 was of a nature not adapted for public reading. 



