Intelligence and Miscellanies. 369 



be interesting to the scholar, as it draws them all upon a 

 uniform plan, and that depending only on the simple princi- 

 ple of the intersection of a cone and a plane. 



1 1 . Description of the Polariscope, an instrument for 

 observing- some of the most interesting phenomena of Po- 

 larised Light,, invented by H. J. Brooke, Esq. F. R. S. 

 &c. ; communicated by Prof. J. W. Webster. 



The term polarised light has been derived from one of the 

 two principal theories concerning the nature of light. 



One of these theories supposes the sensation of light to be 

 produced by the undulations or vibrations, continually suc- 

 ceeding each other, of a very subtle medium, which exists 

 among the particles or within the pores of the hardest bodies 

 as freely as it does in space. And light is thus conceived to 

 be in some measure analogous to sound. 



The other theory supposes light to be material, and to 

 consist of minute solid particles, of each of which two oppo- 

 site sides or ends, as they may be familiarly termed, are en- 

 dued with peculiar properties, and hence, from an imaginary 

 analogy to the poles of a magnet, have been denominated 

 poles. 



It is well known that when light falls obliquely on the pol- 

 ished surface of a transparent body, as glass, one portion of 

 it is reflected from that surface, and another portion is trans- 

 mitted, or passes through the body. 



Thus a portion of the light from the sun which falls on a 

 window, is reflected, and another portion enters and illumin- 

 ates the room. 



It has been found that when light falls at a particular an^ 

 gle upon the polished surface of a transparent body, {this 

 angle however being different for different bodies) both the 

 reflected and transmitted portions acquire new and highly 

 interesting properties totally distinct from those of common 

 light. This change of character is conceived to be produ- 

 ced by the manner in which the particles of light become 

 arranged at the instant of their separation into two portions ; 

 the poles of all the particles of the reflected portion being 

 then supposed to point in one direction, and those of the 

 transmitted portion in another. When the particles of light 

 have been subjected to this supposed regular arrangement 

 the liwht is said to be polarised. 



Vol. XV.— No. 2. 22 



