sense infinitely
small.

Inter-penetration of elements in the production of a chemical
compound, supposes two distinct bodies, A and B, to occupy one and
the same space at the same time. If this were so, different
properties could not consist with an equal and identical
composition.

That hypothesis, however, has shared the fate of innumerable
imaginative explanations of natural phenomena, in which our
predecessors indulged. They have now no advocate. The force of
truth, dependent upon observation, is irresistible. A great many
substances have been discovered amongst organic bodies, composed of
the same elements in the same relative proportions, and yet
exhibiting physical and chemical properties perfectly distinct one
from another. To such substances the term Isomeric (from 1/ao1/
equal and aei1/o1/ part) is applied. A great class of bodies, known
as the volatile oils, oil of turpentine, essence of lemons, oil of
balsam of copaiba, oil of rosemary, oil of juniper, and many others,
differing widely from each other in their odour, in their medicinal
effects, in their boiling point, in their specific gravity, &c., are
exactly identical in composition,--they contain the same elements,
carbon and hydrogen, in the same proportions.

How admirably simple does the chemistry of organic nature present
itself to us from this point of view! An extraordinary variety of
compound bodies produced with equal weights of two elements! and how
wide their dissimilarity! The crystallised part of the oil of roses,
the delicious fragrance of which is so well known, a solid at
ordinary temperatures, although readily volatile, is a compound body
containing exactly the same elements, and in the same proportions,
as the gas we employ for lighting our streets; and, in short, the
same elements, in the same relative quantities, are found in a dozen
other compounds, all differing essentially in their physical and
chemical properties.

These remarkable truths, so highly important in their applications,
were not received and admitted as sufficiently established, without
abundant proofs. Many examples have long been known where the
analysis of two different bodies gave the same composition; but such
cases were regarded as doubtful: at any rate, they were isolated
observations, homeless in the realms of science: until, at length,
examples were discovered of two or more bodies whose absolute
identity of composition, with totally distinct properties