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Steam Engine. 
measure by his professional habits ; and many who in this 
respect pay too great a deference to his authority, have 
adopted this measure as universal and preferable to any 
other. Taking this as a popular measure easy to recol- 
lect, and simple in its application, it undoubtedly has its 
uses ; but in many instances it is inadequate to the pur- 
pose for which it is proposed. The late Professor Robi- 
son has some excellent observations on this subject, in 
the aiticle Machinery^ Sup, Encyclopaedia Britan, where 
he lays down tlie just measure to which the scientific in- 
vestigator will generally have recourse. “ We take, says 
he, for the measure, (as it is the effect) of exerted mecha- 
nical power, the quantity of motion which it produces 
(or whose accumulation it prevents) by its uniform ex- 
ertion during some given time. We say uniform exer- 
tion^ not because this uniformity is necessary", but only 
because, if any variation of the exertion has taken place, 
it must be known in order to judge of the power.” 
A single instance may be adduced, to which the mea- 
sure of Mr. Smeaton is inapplicable, and in which we 
must have recourse to some such measure as that men- 
tioned by Professor Robison. Suppose that a horse while 
standing still sustains by means of a rope and simple fixed 
pulley, a mass of a hundred weight, and thus keeps it sus- 
pended at the top of a well, for the space of a minute. 
Neither the animal nor the vv^eight moves, but shall we 
therefore say, in conformity, as it would seem, with Mr. 
Smeaton’s measure, that there is no power expended, 
and no effect produced ? On the contrary we know there 
is a power expended, and that the effort if sufficiently 
long continued would completely tire the horse. The 
effect which is produced is the annihilation of the simul- 
taneous action of gravity upon the suspended mass ; con- 
sequently, the effect produced is equal, and contrary to 
- the momentum that would be generated by gravity in the 
