crystallized bodies on homogeneous light. 6 1 
Here the virtual pole was coincident with the 5th maximum 
(or thereabouts) of the extraordinary ray from the pole P; 
the succession of tints, however, unless close to the virtual 
pole, is omitted, in order to shorten the table. 
in. 
Table VI. Rochelle salt. Thickness = 0.08557. 
Inclina- 
tions. 
Ordinary peneil. 
Extraordinary. 
Remarks, &c. 
O / 
262 0 
278 O 
Good light pink 
Light blue green . . -j" 
jr 
Pole P for mean 
red. 
Perpendicular 
• • • • • 
i 
incidence. 
Very pale yellow green . 
Bluish purple 
278 20 
Very pale yellow green . 
Violet 
z 78 55 
Very pale bluish green . 
Very light pink,or pinkish white 
280 0 
Indigo . : 
Very pale yellow, almost white 
Pale violet 
Very pale yellow 
281 30 
White 
White, perfectly equal and alike 
Virtual pole. 
Very pale greenish yellow . 
Pale lilac 
N 
OO 
Cn 
Pale greenish yellow 
Sombre lilac purple 
Pale pinkish yellow , 
Dull and impure blue 
Pale pink 
Pale yellow green 
28 5 15 
Crimson 
Yellow green 
285 45 
Rich fiery damask crimson 
Very pale yellow green 
Livid imperfect purple 
Very pale pink yellow 
287 50 
Fine light green 
Fine pink 
288 45 
Very pale green 
Splendid crimson 
Good crimson 
Blue green 
291 40 
Crimson, almost scarlet, &c. . 
Pale blue green, See. 
In this plate the virtual pole fell about half way between 
the 4th maximum and the 5th minimum of the extraordinary 
ray from the apparent pole P for the mean red rays. When 
once more ground down, it gave as follows : 
