r may have while its parts remain together, is
nothing, if compared to the almost incredible power with which its
parts are endued, when they are reduced to vapour by heat. Those
steams which we see rising from the surface of boiling water, and
which to us appear feeble, yet, if properly conducted, acquire immense
force. In the same manner as gunpowder has but small effect, if
suffered to expand at large, so the steam issuing from water is
impotent, where it is permitted to evaporate into the air; but where
confined in a narrow compass, as, for instance, where it rises in an
iron tube shut up on every side, it there exerts all the wonders of
its strength. _Muschenbrook_ has proved by experiment, that the force
of gunpowder is feeble when compared to that of rising steam. A
hundred and forty pounds of gunpowder blew up a weight of thirty
thousand pounds: but, on the other hand, a hundred and forty pounds of
water, converted by heat into steam, lifted a weight of seventy-seven
thousand pounds; and would lift a much greater, if there were means of
giving the steam more heat with safety; for the hotter the steam the
greater is its force.

_Artificial Memory._

In travelling along a road, the sight of the more remarkable scenes we
meet with, frequently puts us in mind of the subjects we were thinking
or talking of when we last saw them. Such facts, which were perfectly
familiar, even to the vulgar, might very naturally suggest the
possibility of assisting the memory, by establishing a connexion
between the ideas we wish to remember, and certain sensible objects,
which have been found from experience to make a permanent impression
on the mind. It was said, that a person contrived a method of
committing to memory the sermons which he was accustomed to hear, by
fixing his attention, during the different heads of the discourse, on
different compartments of the roof of the church, in such a manner as,
that when he afterwards saw the roof, or remembered the order in which
its compartments were disposed, he recollected the method which the
preacher had observed in treating his subject. This contrivance was
perfectly analogous to the topical memory of the ancients; an art
which, whatever be the opinion we entertain of its use, is certainly
entitled, in a high degree, to the praise of ingenuity.

Suppose you fix in your memory the different apartments in some very
large building, and that you had accustomed yourself to think of