228 Proceedings of Philosophical Societies. ([Mancny, 
crystals of fluor spar and common salt, in certain cases, depolarize 
light, in others not. Whenever-any deviation from the exact figure 
of the crystal takes place, they acquire the pewer of depolarizing ; 
and this deviation may be either towards the side of attraction or re- 
ulsion. 
On Thursday, the 15th of February, a paper by Mr. Tod, surgeon 
in the navy, was read, containing some experiments and observations 
on the torpedo electricus. While the ship Lion, in which Mr. Tod 
was, lay at the Cape of Good Hope, a considerable number of this 
fish was caught by the seine, but none by the line, though they fished 
with every kind of bait in the very place where the fish was caught 
by the seine. When caught it was put into a tub of water, where it 
lived usually three, and in one case, five days, Mr. Tod in the paper 
gives a description of the fish, and mentions its general size, which 
is known to be small. The fish discharged the electric energy at 
pleasure, and it ceased with the life of the animal. When caught 
it attempted in the first place to make its escape by muscular exer- 
tion, and did not exert its electric energy till it found the first at- 
tempt unsuccessful. A motion of the eye of the fish was generally 
perceptible when it exerted this energy, so that Mr. Tod could ge- 
nerally tell when the shock was given to another person who held 
the animal in his hand; the shock never reached farther than the 
shoulder, and often not farther than the elbow. 
At the same meeting, two papers by the Rev. Abram Robertson, 
D.D. F.R.S. were announced: the first giving a method of calcu- 
lating the excentric from the mean anomaly of a planet ; the second 
containing a demonstration of Dr. Maskelyne’s method of finding 
the longitude and latitude of a celestial object from its right ascen- 
sion, and vice versd ; and pointing out two mistakes to which Dr, 
Maskelyne’s method is liable. 
On Thursday, the 22d of February, a paper by Sir Everard Home 
was read, giving an account of the mechanism of the feet of an East 
Indian species of lizzard, which is capable, like the common fly, of 
walking up and down the perpendicular face of smooth walls without 
falling. ‘This mechanism consists in a particular muscular con- 
trivance, by which a quantity of air contained between the wall and 
the foot of the animal, enclosed within a kind of cartilaginous ring, 
is rarefied so much as to enable the foot of the animal to adhere with 
sufficient force to support the whole weight of the body. This rari- 
faction is continued without any muscular exertion after it has once 
taken place. There can be little doubt that the foot of the fly is 
constructed in the same way, though its size is so small that nothing 
can be determined by inspecting it with the naked eye. When high 
magnifying powers are employed, the observer is so liable to be de- 
ceived by appearances that nothing very precise can be determined 
on the subject. 
LINNEAN SOCIETY. 
At the meetings of the society.on the 6th and the 20th of Fe- 
. 
