340 Mr Herschel on the Demations from New lories Sccik 
sphaerometer, and found respectively 165900 and 94499 miL 
lionths of an inch. On examining them separately in polarized 
light, I was now much astonished to find the rings exhibited by 
the two portions, though both circular, yet differing altogether 
in their characters. Those in the thicker portion were in every 
respect precisely analogous in the scale of their tints, to those of 
that variety with one axis, which seems to form the central por- 
tion and upper lamina of Dr Brewster’s Tesselite^ and of which 
I need not here particularise the succession of colours, as it is 
given at full length in my paper above alluded to. On the 
other hand, the rings in the thinner portion exhibited a com- 
plete inversion of the Newtonian Scale, the red rays being more 
energetically acted upon than the violet, and that to so extraor- 
dinary a degree, that the whole prismatic spectrum was display- 
ed in the very first ring. 
To obtain a sufficient range of incidence, this plate was inclo- 
sed in olive oil, in a proper apparatus for measuring the inclinar. 
lion, and being exposed to polarized light, (the plane of inci- 
dence 45® inclined to that of primitive polarization,) the succes- 
sion of tints, and their corresponding angles of incidence were 
as in the following Table, in which the angles are deduced from 
two observations of the same tint on opposite sides of the axis. 
The measures of length in this and the subsequent pages are in 
millionths of an inch, for the sake of placing in evidence their 
proportion to the lengths of the fits of easy transmission and 
reflexion. 
Table II. — Second variety of Apophyllite in olive oil. Index 
of refraction 1 .0497. Thichness of the plate — 94499- 
Incidence. 
Ordinary Pencil. 
Extraordinary Pencil. 
0® O' 
White. 
Black. 
White. 
Sombre orange-red. 
White. 
Pretty good orange. 
Very light blue. 
Good orange-yellow. 
Sky-blue. 
Fine orange-yellow. 
Fine deep indigo^ 
Fine light yellow. 
23 35 
Rich dark purple. 
Pale yellow. 
Fine crimson. 
Light greenish-yellow. 
2r 11' 
Fine pink. 
Fine light green. 
28 48 
Pink, somewhat inclining to brick- 
Good bluish-green {maximum of 
red. 
contrast). 
Light pink, inclining to orange. 
Blue, rather greenish. 
Pale pink yellow. 
Dirty and sombre blue. 
33 2 
Y ellowish-white. 
Dull, indifferent purple. 
