118 Notice of some Recent 



Mr.- Boyle found, that a piece of amber would become 

 electrified by exposure to a sunbeam. Mr. Draper pro- 

 duced the same effect on ruby from Ceylon, rolled sap- 

 phire, a tourmaline, a Brazilian emerald, a topaz, and 

 likewise glass. He attributes this to the agency of the 

 light, and not to the heat ; because, when exposed to the 

 action of heat from another source, in the same degree, no 

 such consequence followed. 



5. Absorption of light. — The remarkable phenomena dis- 

 covered by Sir David Brewster, of absorption in light, 

 which has passed through certain coloured gases have been 

 examined by Wrede.* According to him, one part of the 

 light is retarded relatively to the other part, in a quantity 

 proportionate to the nature of the body; and which, con- 

 sequently, must be different in different bodies. If this 

 hypothesis is admitted, then the phenomena discovered by 

 Brewster follow, as a necessary consequence. Without 

 presuming to explain in what way this retardation takes 

 place, Wrede has calculated its effects on three different 

 suppositions; 1. on the supposition of a simple retardation; 

 2. on the supposition of an infinity of partial reflexions, 

 between the particles of matter analogous to those which 

 take place between the two plain surfaces of a translucid 

 body; and, 3. on the same supposition extended to a great 

 number of particles, that is to say, supposing the influence 

 of bodies upon light, will be the same as that of a great 

 number of plain and equi-distant surfaces. M. Wrede has 

 constructed the formulae representing the resultant inten- 

 sity, by taking for the abscissa of the constructed curve, 

 the logarithms of the proportions between the retardation 

 and the lengths of the undulation, and for the ordinates 

 the corresponding intensities. The resulting curve re- 

 sembles somewhat a spiral wire. 



The difference between the logarithms of the two num- 

 bers, being independent of the absolute values of these 

 numbers, the distance between two points of the axis of 

 the abscissa, which correspond to the limits of the spec- 

 trum, ought to be the same, whatever the extent of the 

 retardation is ; it is clear, that this distance ought to be 

 equal to the logarithm of the proportion between the 



* Bibliotheque Universelle, June, 1835. 



