410 DR BREWSTER on the Refractive Powers, and other 



The following Table will shew the relations of the indices of 

 refraction of these two new substances to those of other bodies 

 which I have found to possess a refractive power lower than 

 Water. 



TABLE of Refractive Powers lower than Water. 



Water, 1.3358 



Cyanogen* rendered fluid by pressure, 1.316 



Ice, 1.3085f 



Second New Fluid in Topaz, in a cavity which 

 is filled by the other new fluid, at the tem- 

 perature of 83 1.2946 



New Fluid in Amethyst, which fills the cavity 



at a temperature of 83* of Fahrenheit, 1.2106 



Tabasheer, whitish, from Nagpore, hard speci- 

 men, 1.1826 



Tabasheer, transparent, from Nagpore, 1.1503 



Do. do. another specimen, 1 .1454 



New Expansible Fluid in Topaz, in the same 

 cavity as the second fluid, whose index of re- 

 fraction is given above 1.1311 



Transparent Tabasheer from Vellore, of a yel- 

 lowish tint, 1.1111 



Ether e'xpanded into nearly thrice its original 



bulk, 1.057 



I have not made any attempt to measure the refractive power 

 of the new expansible fluid, after it has filled the cavity, having 

 satisfied myself with observing, that the angle of total reflexion 

 diminished when the fluid was in this expanded state J. In 



* This Cyanogen was made by Dr TURNEB. Mr FAKADAY, who first rendered it 

 fluid, remarks " that its refractive power is rather less, perhaps, than that of water." 

 Phil. Trans. 1819, p. 286. 



f- This is a mean between Dr WOI.LASTON'S result and mine. 



{ This experiment is a very interesting one to the spectator ; the new fluid, ap- 

 pearing quite transparent at a temperature of 60, seems quite opaque when it is 

 made to fill the tube, by a slight increase of temperature, as if it had become black 

 by heat. 



