464 Analyses of Books. [Jone, 
Ascension and Declination, the Obliquity of the Ecliptic being given 
in both Cases. By the Rev. Abram Robertson, D.D. 
9. Some Account of the Feet of those Animals whose progressive 
Motion can be carried on in Opposition to Gravity. By Sir Everard 
Home, Bart. V.P.R.S. 
The common house fly, it is well known, can walk with facility 
up the perpendicular surface of panes of window glass, and even 
upon the ceiling of the room, thus supporting itself contrary to 
gravity. But the foot of this animal is so small, that its anatomical 
structure cannot be ascertained. But the lacerta gecko, a native of 
Java, possesses a similar power. It is an animal of considerable 
size, weighing above 50z. The author obtained a specimen of this 
animal from Sir Joseph Bankes, and was enabled in consequence to 
ascertain the structure of its foot. Each foot has five toes, which 
terminate each in a crooked claw. ound the toe there are a set of 
transverse openings or pockets with serrated edges. When these 
serrated edges attach themselves to the wall, the pockets are ex- 
tended by a set of muscles adapted for the purpose. A vacuum of 
course is formed ineach. ‘lhe consequent pressure of the air is 
sufficient to keep the foot attached to the wall, and to support the 
weight of the animal. The structure of the top of the head of the 
echineis remora, or sucking fish, is similar. By means of it the 
animal keeps itself attached to the shark, or to the bottom of ships. 
There can be no doubt that the structure of the feet of flies must 
be similar. 
10. On the Communication of the Structure of doubly refracting 
Crystals to Glass, Muriaie of Soda, Fluor Spar, and other Sub- 
stances, by mechanical Compression and Dilatation. By Dr. 
Brewster. 
When the edges of a plate of glass are pressed together by any 
kind of force, it exhibits distinct neutral and depolarizing axes, like 
all doubly refracting crystals, and separates polarized light into its 
‘complementary colours. The neutral axes are parallel and perpen- 
dicular to the direction in which the force is applied, and the depo- 
larizing axes are inclined to these at angles of 45°. Whena plate 
of glass is bent by the hand, one side of it is compressed, and the 
other dilated. The compressed side has a structure the same as that 
of calcareous spar, beryl, &c. while the dilated side has a structure 
similar to that of quartz, sulphate of lime, &c. 
Common salt, fluor spar, and other similar bodies, acquire the 
same structure by compression and dilatation. But compression and 
dilatation produce no change in the structure of those bodies that 
already possess the property of refracting doubly. 
Compression and dilatation produce the same effects upon animal 
jelly as upon glass. 
11. An Essay towards the Calculus of Functions, Part II. By 
Charles Babbage, Esq. 
12, Experiments and Observations to prove that the beneficial 
Effects of many Medicines are produced through the Medium of 
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