refractive and dispersive Powers. 377 
appears to exceed the metallic oxides in dispersive power, the 
latter is inferior even to water. 
As I have likewise, at various times, made many experiments 
on dispersion by means of wedges, in a manner nearly similar 
to that employed by Mr. Dollond, Dr. Blair, and others, I 
have endeavoured to reduce the several substances thus exa- 
mined to one table ; but, as the limits of colour are in few in- 
stances sufficiently well defined for accurate mensuration, I have 
not attempted to add any numerical estimate of their powers, 
but have merely ascertained the order in which they succeed 
each other; and, in the following table, have arranged them 
according to the excess of their effect on violet above red light, 
at a given angle of deviation. 
Table III. 
Order of dispersive 
Powers. 
Refr. Power. 
Sulphur - - 2,04 
Glass of lead (i. sand) 1,987 
Balsam of Tolu - 1,60 
Oil of sassafras - - 1,336 
Muriate of antimony 
Guaiacum - - 1,396 
OiJ of cloves - - 1,333 
Flint-glass - - 1,386 
Colophony - - 1,543 
Canada balsam - 1,328 
Oil of amber - - 1 ,303 
Jargon - - 1,95 
Oil of turpentine - 1,47 
Copal - - - 1,535 
Balsam of capivi - 1 j3°7 
Anime - - 1 * >.~ 
T , , 1 ’0OO 
Iceland spar - - 1,637 
Order of dispersive 
Powers, 
Amber 
Diamond 
Alum 
Plate-glass, Dutch 
Ditto, English 
Crown glass 
Ruby (spinelle) 
Water 
Sulphuric acid 
Alcohol - 
Sulphate of barytes 
Selenite 
Rock crystal 
Sulphate of potash 
White sapphire 
Fluor spar 
Refr. Power. 
5.547 
~ 2,44 
- 1 , 4*57 
- i,5 1 7 
D3° 4 
- C533 
1,812 
M 35 
■ 1 -37 
- 1,046 
R525 
- i,547 
• 1 , 4*95 
3,768 
- M33 
