fibres of which it is composed; and that the velocity and motion
of a muscle consists in the length and extent of its fibres. Let
us compare this doctrine with the language of the jockey: he tells
us, if a Horse has not length, he will be slow; and if made to
slender, he will not be able to bring his weight through. Does
not the observation of the jockey exactly correspond with this
doctrine? If we now inquire into the motion of Horses, we shall
find the bones are the levers of the body, and the tendons and
muscles (which are one and the same thing) are the powers of
acting applied to these levers. Now when we consider a half-bred
Horse running one mile or more, with the same velocity as a Horse
of foreign extraction, we do not impute that equality of velocity
to any innate quality in the half-bred Horse, because we can
account for it by external causes: that is by an equality of the
length, and extent of his levers and tendons. And when we consider
a half-bred Horse running one mile, or more, with the same
velocity as the other, and then giving it up, what shall we do?
shall we say the foreigner beats him by his blood, or by the force
and power of his tendons? or can we, without reproaching our own
reason and understanding, impute that to be the effect of occult
and hidden causes in the one of these instances and not in the
other? both of which are demonstrated with certainty, and reduced
to facts by the knowledge of anatomy and the principles of
mechanics.

How many instances have we of different Horses beating each other
alternately over different sorts of ground! how often do we see
short, close, compact Horses beating others of a more lengthened
shape, over high and hilly coursed, as well as deep and slippery
ground; in the latter of which, the blood is esteemed much better,