Chemical Science. | 175 
galvanic combination; the limbs of a newly-killed frog underwent’ 
evident convulsions when made part of the circuit. 
In order to remove any source of fallacy that might have at- 
tended the employment of a metallic wire to connect the charcoals, 
another apparatus was made.in which they were united into arcs 
by cotton or silk threads, and upon examining it by the tongue 
and the limbs of a frog, the effects were similar to those before 
preduced in the first form of experiment. 
Upon making a tube filled with water part of the circuit, a de- 
composition was expected, but none took place, although the ex- 
periment continued several hours, nor would it revive copper from 
its solution in sulphuric, or acetic acids, so that its respective 
poles have not been distinguished. 
In all experiments made with this apparatus, the employment of 
metals was carefully excluded, so that their contact with the 
charcoal should not give incorrect results. 
If when the limbs of a frog are undergoing convulsions, one of 
the arcs be removed from the circuit, they instantly cease, but re- 
turn again, upon its being replaced; and it is a curious fact that 
the effect on the limbs is decidedly most powerful, when the nerve 
is in contact with the rapidly absorbing surface; if the opposite 
arrangement be adopted making the muscle in contact with it, the 
effect is greatly diminished, or altogether ceases. 
That the activity of the apparatus is dependent upon the ab- 
sorption of water, is proved by its cessation in about twenty-four 
hours, the charcoals becoming saturated with water ; but by heating 
them red hot it is expelled, and upon again arranging them in the. 
manner mentioned, they will be found to regain their former ac- 
tivity. 
A solution of common salt, being employed as the fluid, aug- 
ments the effect of the apparatus, it being a better conductor; but 
if it is wished to heat the charcoals for another experiment, they 
should be soaked in water to dissolve the salt, which would other- 
wise fuse, and fill up the pores. ‘The woods from which the char- 
coals are obtained, are known by the names of Botany Bay, and 
King wood. The former should be chosen full of dark streaks, 
which open when exposed to heat, and give the resulting char- 
coal a great degree of porosity. In selecting the other wood, no 
very particular attention is required, it generally producing a 
charcoal of pretty uniform density. 
II. Naruran History. 
1. Vegetation at different Heights.—The following is a table 
constructed by Mr. Bakewell, of the height at which various trees 
and shrubs grow in the Vallois and Savoy. The extreme height 
