As this is the universal term used to express the capability of first movers, of magnitude, it is essential that the estimate of it should be uniform.

Its estimate is the elevation of 33,000 pounds avoirdupois one foot in height in one minute, and it is designated as being Nominal, Indicated, or Actual.

The first designation being adopted and referred to by Manufacturers of steam engines in order to express the capacity of an engine, the elements thereof being confined to the dimensions of the steam cylinder, and a conventional pressure of steam and speed of piston; the second to designate the full capacity of an engine, as developed in operation, without any deduction for friction ; and the last referring to its actual power as developed by its operation, involving the elements of the mean pressure upon the piston, its velocity, and a just deduction for the friction of the operation of the machine.

In reviewing the various modes for the computation as submitted by Engineers and Manufacturers, there is no proper formula that presents the essential element of being in conformity with any other, and as conformity in a rule for this purpose, if based upon an assimilation to the capacity of an engine, is all that is requisite, it would have been preferable to have adopted an existing formula to the introduction of a new one, had it been practicable to have done so. It occurs, further, that there is not only a want of conformity in the various rules essayed by authors, but they have neither reached the cases of both condensing and non-condensing engines, nor have they properly approached to the actual power of an engine; and as the practice of operating engines since the adoption of existing formulae has materially altered, both in an increase of pressure and velocity of piston, the following rules are submitted.