perfect philosophy of the moral or metaphysical kind serves only to
discover larger portions of it. Thus the observation of human blindness
and weakness is the result of all philosophy, and meets us at every
turn, in spite of our endeavours to elude or avoid it.

27. Nor is geometry, when taken into the assistance of natural
philosophy, ever able to remedy this defect, or lead us into the
knowledge of ultimate causes, by all that accuracy of reasoning for
which it is so justly celebrated. Every part of mixed mathematics
proceeds upon the supposition that certain laws are established by
nature in her operations; and abstract reasonings are employed, either
to assist experience in the discovery of these laws, or to determine
their influence in particular instances, where it depends upon any
precise degree of distance and quantity. Thus, it is a law of motion,
discovered by experience, that the moment or force of any body in motion
is in the compound ratio or proportion of its solid contents and its
velocity; and consequently, that a small force may remove the greatest
obstacle or raise the greatest weight, if, by any contrivance or
machinery, we can increase the velocity of that force, so as to make it
an overmatch for its antagonist. Geometry assists us in the application
of this law, by giving us the just dimensions of all the parts and
figures which can enter into any species of machine; but still the
discovery of the law itself is owing merely to experience, and all the
abstract reasonings in the world could never lead us one step towards
the knowledge of it. When we reason _a priori_, and consider merely any
object or cause, as it appears to the mind, independent of all
observation, it never could suggest to us the notion of any distinct
object, such as its effect; much less, show us the inseparable and
inviolable connexion between them. A man must be very sagacious who
could discover by reasoning that crystal is the effect of heat, and ice