1816.] 
Ambergris melted and cooled. 
Film of hydatids. 
Film lining the ribs of a lamb. 
Film from the stalks of rhubarb. 
Film covering the shell solen 
ensis. 
Resin of bile melted and cooled. 
Jelly from calves feet. 
Skin of a fowl. 
Scale from the body of a bee. 
Hair of a bee. 
Wing of a bee. 
Wing of a house beetle. 
Wing of the May fly. 
Wing of the stone fly. 
Hair from the pinna marina. 
Wing of the meloe vesicatorius. 
Film covering the stem of leon- 
todon taraxicum. 
Film between the coats of an 
onion. . 
Film of the leaf of American 
houseleek. 
Leaf of the hydrangea. 
during the Year 1815. 
A 
“tT 
Spatha of a lily. 
Film of gum-arabic. 
Rosin. 
Copal. 
Thin fragments of gum-animé. 
Galbanum. 
Gum Juniper. 
Canada balsam indurated. 
Sphere of sea weed. 
Film on the stalk of fleur de lys. 
Thin slices from a wafer. 
Pappus of leontodon taraxicum. 
Film lining the shell of an egg. 
Skin of a dried grape. 
Phosphorus. 
Hair from the fur of a seal. 
Skin of an infant eleven months 
old. 
Skin of a child two months before 
birth. 
Skin of a herring. 
Mastich. 
Burgundy pitch. 
Dr. Brewster has shown that the modes in which bodies depo- 
Jarize light may be reduced to seven :-— 
(1.) When the crystal possesses neutral axes, and forms two 
images which are capable of being rendered visible, as in calcareous 
spar, topaz, &c. 
(2.) When the crystal possesses neutral axes, and exhibits only a 
single image, as the human hair, and various transparent films. 
(3.) When the crystal has no neutral axes, but depolarizes light 
in every position, as in gwm-arabic, caoutchouc, tortoise-shell, &e. 
(4.) When there is an approach to a neutral axis, as in goldleaters’ 
leaf, &c. 
(5.) When the crystal depolarizes, or restores only a part of the 
polarized image, as in the film of sea weed and a film from the 
crab. 
(6.) When the crystal depolarizes luminous sectors of nebulous 
light, as the oil of mace. 
(7.) When the crystal restores the vanished image, but allows it 
to vanish again during the revolution of the calcareous spar. 
Our author gives a theory of these different kinds of depolariza- 
tion, and endeavours to reduce them all to the first kind. 
3. Dr. Brewster discovered that when calves-foot jelly or coagu- 
lated isinglass is exposed to pressure, it acquires the property of de- 
polarizing light, and loses it again when the pressure is removed. 
Thus it appears that by pressure these bodies acquire a crystallized 
texture, 
9 
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