ii6 Imperial Institute of France. 



object-glasses, is entirely identical with that which the re- 

 flection communicates to them ; so that, for instance, if in 

 a determinate position of the objccl-glasses and of a crystal, 

 when we look at the reflected rings, we onlv perceive the 

 image of the rinjrs which proceed from the extraordinarv 

 refraction, it will still be the extraordinary image which we 

 shall perceive, when in similar circumstances we shall 

 examine the rings transmitted. This result, which M. 

 Arago connniinicated to the Class in the montbof February, 

 seems to prove that the coloured rings are formed solely at 

 the expense of the light, which in the presence of the se- 

 cond lens will be partially reflected, and thus establishes 

 an intimate connection between these two most extraor- 

 dinary classes of the phaenomena of optics. 



On the nth of March, M. Malus announced to the 

 Class, that on subjecting, at various times, the light which 

 the glasses transmit under an angle of 35^ 25', he had 

 ascertained that this light is composed of a certain quantity 

 of rays polarized in a direction contrary to the reflected 

 rays, and of another portion of rays not modified, which 

 preserve the properties of the direct light : this last portion 

 diminishes at each new transmission of the fasciculus ; so 

 that, if we pass through a pile of parallel glasses, the por- 

 tion of light transmitted is entirely polarized in one direc- 

 tion, while the rays successively reflected are polarized in a 

 contrary direction. M. Mains concludes from this, that 

 at all times, when by any contrivance we produce a ray 

 polarized in one direction, we necessarily obtain a ray 

 polarized in a direction diametrically opposite, and that 

 these rays follow different routes. The observation of M. 

 Arago, which we have recently mentioned, forms the only 

 exception to this genjeral rule, since the rings reflected and 

 transmitted are polarized in the same manner. 



M. Arago had long ago ascertained that diaphanous and 

 opake bodies modify the light which they reflect : the me- 

 tallic bodies alone seemed to him to impress no new pro- 

 perty. It is true that opticians were well aware that there 

 was a sliglit difierence between the intensity of the twor 

 images formed by a rhomboid, by the help of rays reflected 

 bv a metallic plane : but this isolated fact could teach us 

 nothing relative to the particular mode of action of the 

 metallic bodies and of light. But in a memoir read to the 

 Institute on the 27th of May 1811, M. Malus has shown, 

 by experiments made on rays already polarized, and by the 

 help of a method of which it would be difficult to give a 

 clear idea in an extract, that the light reflected by the me- 

 tals 



