THE 



PHILOSOPHICAL MAGAZINE 



AND 



ANNALS OF PHILOSOPHY. 



[NEW SERIES.] 



MARCH 1832. 



XX. Tlieory of the Transmission of Light through Mediums^ 

 and of its Reflection at their Surfaces, accordi7ig to the Hy- 

 pothesis of Undulations. By the Rev. J. Challis, Fellow of 

 the Cambridge Philosophical Society*. 



TN a communication to the Philosophical Magazine and 

 *- Annals for May 1830, I ventured to suggest that the dimi- 

 nished velocity of the transmission of light in the interior of 

 mediums miglit be solely owing to the obstacles to the free mo- 

 tions of the ethereal particles, occasioned by the presence of 

 the atoms of the mediums. This idea was not supported by all 

 the reasons that may be advanced in its favour, because I was 

 not then prepared with a simple mode of exhibiting them. I 

 hope now to be able to show in an intelligible manner how the 

 cause alleged in this view may produce the effect ascribed to it. 

 The suppositions that will be made for this purpose are 

 the same that I stated in a previous communication to this 

 Journal, respecting the different refrangibility of the rays of 

 light+ ; viz. that the aether, which is the vehicle of light, is con- 

 stituted like air; that it permeates all mediums, and has the 

 same density in them as out of them ; and that uniform and 

 homogeneous mediums (which for the sake of simplicity are 

 the only ones here considered) consist of very minute material 

 atoms, definitely arranged, all of the same weight and size, 

 spherical in shape, an d so close to eacliother that a very 

 great number are included in a cubical space the side of which 

 is a 50,000th part of an inch, yet on account of their small 

 magnitude occupying a portion of space very small compared 

 to the intervening spaces. 



• Communicated by the Author . 

 t Sec Phil. Miig. and Annals, N.S. vol. viii. p. 172. 

 N. S. Vol. 1 1 . No. G3. March 1 832. Y For 



