44+ Dr. Brewster’s experiments on the 
Resin of bile melted and cooled. 
Jelly from calves’ feet. 
The 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. 
The byssus, or hair from the pinna marina. 
Wing of the meloe vesicatorius. 
Film which covers the tubular stalk of the 
leontodon taraxacum. 
Film between the coats of an onion. 
Film on the leaf of the American house 
leek. 
Leaf of the hydrangea. 
Spatha of a lily. 
Film of gum Arabic formed by evapora- 
tion. 
Rosin. 
Gum copal. 
Thin fragments of gum anime. 
Gum galbanum. 
Gum juniper. 
Canada balsam indurated. 
The spheres on sea-weed. 
Film which lines the stalk of the Jieiir dt 
lys. 
Thin slices from a wafer. 
Filaments of the pappus of the leontodon 
taraxacum. 
Film which lines 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. 
Gum mastic. 
Burgundy pitch. 
II. Theory of the depolarisation of light. 
The various modes in which bodies depolarise light may be 
reduced to seven. 
1. When the oystal possesses neutral axes, and forms two 
images which are capable of being rendered visible, as in cal- 
careous spar, topaz , he. 
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 depolarises 
light in every position, as in gum Arabic , caoutchouc, tortoise 
shell , he. 
