24 PAPERS, ETC. 
battery was used, nor metal in its metallic state. It was 
simply a close imitation of nature, but followed out only 
for a year, whereas nature has at her command unlimited 
time and resources. Now as we find the great body of 
amorphous and crystalline formations which exist in the 
subterranean fissures or lodes to exist at amore or less 
considerable distance from the surface of the earth, and as 
the subterranean heat is found to increase pretty regularly 
from a few feet beneath the surface to the greatest depth 
which has been sunk, we may conclude that the tem- 
perature in which they are found is most congenial to 
their formation, as well as is the uniformity of such 
temperature. In fact, I commonly find in my artificial 
processes, whether I employ a higher or lower temperature, 
that it is desirable it should be as even as possible, 
thereby corresponding to the conditions under which they 
make their appearance in nature. I think, with many 
others, that the existence of a central fire within our globe 
is hishly probable, and likewise that such heat is nearly 
constant ; or, ifin a state of gradual diminution, that such 
diminution is extremely slow and regular, and not cal- 
eulated to produce appreciable changes in the course of 
some centuries. The presence or absence of light occasions 
a very considerable difference in the electrical formation 
of erystals, both as regards their form, the size of each 
erystal, its solidity, the space over which they extend, and 
their adhesiveness to the substance upon which they grow. 
In some instances exposure to daylight altogether prevents 
the desired formation. I have found this to be the case 
with respect to sulphate of strontia. An apparatus calcu- 
lated to produce such a formation was exposed for two 
months in aroom with a southern aspect, but not a single 
erystal made its appearance on the southern side, and but 
