CHEMISTRY. 
It is true, indeed, that such admissions 
are generally made with a previous notice 
or reservation of this uncertainty. But by 
the constant use of the supposed facts, 
along with others which are better esta- 
blished, the mind becomes habituated to 
mix hypotliesis with facts ; and the imagina- 
ry beauty of connected science must from 
time to time be destroyed by the appear- 
ance of new truths. The revolutions of 
chemical Science have amply shown this ; 
and the numerous imperfections which stilt 
remain have left considerable latitude for 
the arrangement of materials in a system of 
chemistry. If the theoiy were in its com- 
mencement, a treatise on chemistry would 
be little more than a collection of receipts 
for' processes ; and even in the present 
state of the science, different authors of 
credit and respectability greatly differ in 
the disposal of their subjects. Operative 
chemistry usually precedes the theory in 
the earlier works. Some writers treat of 
compound bodies, and deduce their princi- 
ples or component parts in the way of ana- 
lysis; while others begin with the habi- 
tudes or powers by which the several 
changes are effected. But it must be con- 
fessed, notwithstanding the magnitude of 
the discoveries which have been really 
made, and the elevated pretensions of a few' 
theorists, that the practical science is still in 
its infancy. Every one of the phenomena is 
sufficiently complicated as to be referable 
to various topics of consideration ; and to 
which of these in a general way our atten- 
tion shall be first directed, is in many cases 
a matter of indifference. It appears to us 
that the advantages of treating the subjects 
in a popular way, by first attending to the 
general properties and habitudes of bodies, 
and the methods of operating upon them, 
and from thence proceeding to the different 
classes of bodies, are such as entitle this 
method to a preference before other ar- 
rangements which afford a greater appear- 
ance of synthetical order. 
When we have simplified our notions of 
the causes of change which happen to bo- 
dies under the distinction or division of 
chemistry, we must resolve them into two, 
namely, heat and attraction. Daily expe-' 
rience shews us that bodies may be more of 
less heated, and also tliat they adhere 
to each other. We are in truth unable 
to proceed far ther in our abstractions. The 
causes of those well known effects have not 
yet been developed by the manifestation of 
any more simple facts upon which they 
may depend. We can only observe the ' 
laws according to which these powers have 
been found to act, and make our classifica- 
tion of the phenomena ; and as it is of some 
utility, in directing our future researches, to 
make conjectures by analogy, it may also 
be permitted to speculate upon the causes 
of these primary effects, provided it be done 
with caution, and without that bigotry which 
even in systems of philosophy has so fre- 
quently established the results of error. 
Besides the effects of heat and attraction, 
we find that bodies are changed and modi- 
fied by light, electricity, galvanism, and 
magnetism, the three last of which are ac- 
companied by attraction or repulsion. But 
as these are much less generally applicable 
in operative chemistry than the powers first 
mentioned, and as it seems likely that future 
discoveries may lead to some intimate rela- 
tion, or perhaps show the identity of the 
cause of heat, light, and the other affections 
of matter which have here engaged our at- 
tention, it is unnecessary to enlarge upon 
these in the present article. 
The word attraction denotes the unex- 
plained tendency which bodies have to 
move to each other. We observe it acting 
at a jiistance in the fall of bodies on tlie 
surface of the earth, and in the motions of 
the heavenly bodies, as well as in such as 
are affected by electricity, galvanism, or 
magnetism : and in the cohesion which 
gives solidity, or, more properly, rigidity to 
bodies, as well as in those effects wherein 
the parts of different bodies unite to form 
new compounds, we deduce its effects 
from motions or actions which cannot be 
sepai’ately distinguished. And these dif- 
ferences, though they cannot be shown to 
arise from one and the same power, or from 
energies originally dissimilar, require at least 
for the purposes of language to be treated 
apart from each other. Chemistry seems 
to have little to do with the perceptible at- 
tractions : it is principally confined to the 
state of bodies, as it relates to the cohesion 
and the combination of their parts. 
Heat, or rather temperature, is a well 
known modification of bodies, by which 
they produce a peculiar sensation distin- 
guished by the same word. Its laws have 
been very successfully investigated by our 
contemporaries ; for which see Caloric, 
Heat, and Combustion. The operative 
chemist considers it as the means of con- 
verting solid bodies into dense fluids', and 
dense fluids into elastic fluids called gas 
or vapour, while compound bodies may 
