In the same connection the _form_ of engine to be used must be
considered. In some few cases--as, for instance, where engines have to
be placed in confined situations--the form is practically fixed by the
space available, it being perhaps possible only to erect a vertical or a
horizontal engine, as the case may be. These, however, are exceptional
instances, and in most cases--at all events where large powers are
required--the engineer may have a free choice in the matter. Under
these circumstances the best form, in the vast majority of cases where
machinery must be driven, is undoubtedly the horizontal engine, and the
worst the beam engine. When properly constructed, the horizontal engine
is more durable than the beam engine, while, its first cost being less,
it can be driven at a higher speed, and it involves a much smaller
outlay for engine house and foundations than the latter. In many
respects the horizontal engine is undoubtedly closely approached in
advantages by the best forms of vertical engines; but on the whole we
consider that where machinery is to be driven the balance of advantages
is decidedly in favor of the former class, and particularly so in the
case of large powers.

The next point to be decided is, whether a condensing or non-condensing
engine should be employed. In settling this question not only the
respective first costs of the two classes of engines must be taken into
consideration, but also the cost of water and fuel. Excepting, perhaps,
in cases of very small powers, and in those instances where the exhaust
steam from a non-condensing engine can be turned to good account for
heating or drying purpose, it may safely be asserted that in all
instances where a sufficient supply of condensing water is available
at a moderate cost, the extra economy of a well-constructed condensing
engine will fully warrant the additional outlay involved in its