288 
Dr. Brewster on the optical 
Quartz, - Malus 54 14.57 
Calcareous spar, Malus 6423.5 
Flint glass, lowest 
7238. 
Ruby 
7388.8 
Brazilian topaz 
7586.7 
Water, - Malus 
*0 
00 
1 ^ 
Flint glass, highest 
8735- 
Carbonate of potash 
10227. 
Chromate of lead 
10436. 
Nitre 
11362. 
Muriate of soda - 
12086. 
Bees wax, - Malus 
13308.1 
Diamond, - Malus 
*39%5 
Sulphur 
22000. 
Phosphorus 
28857. 
Hydrogen 
29364. 
... — — 
31862. 
It appears from the preceding table, that tabasheer, which 
was placed between water and air, in the comparison of their 
indices of refraction, is now not only the lowest of all sub- 
stances in its absolute refractive power, but it is so extremely 
low as to be separated by a great interval from them all. 
The very high refractive power of sulphur, phosphorus and 
hydrogen, and the great interval between diamond and sul- 
phur are very remarkable, and indicate that hydrogen may 
enter largely into the composition of sulphur and phosphorus. 
I now saturated the prism of tabasheer with water and with 
oil of cassia in succession, and I found that, in the first case, 
its refractive power was raised to 1.4012 higher than that of 
water, and in the second case to 1.6423, a little greater than 
