give
any directions, the use of the treatise being only to teach the proper
method of imitating the figures which are annexed. It will be proper to
incite the scholars to industry, by showing in other books the use of
the art, and informing them how much it assists the apprehension, and
relieves the memory; and if they are obliged sometimes to write
descriptions of engines, utensils, or any complex pieces of workmanship,
they will more fully apprehend the necessity of an expedient which so
happily supplies the defects of language, and enables the eye to
conceive what cannot be conveyed to the mind any other way. When they
have read this treatise, and practised upon these figures, their theory
may be improved by the Jesuit's Perspective, and their manual operations
by other figures which may be easily procured.

7. Logick, or the art of arranging and connecting ideas, of forming and
examining arguments, is universally allowed to be an attainment, in the
utmost degree, worthy the ambition of that being whose highest honour is
to be endued with reason; but it is doubted whether that ambition has
yet been gratified, and whether the powers of ratiocination have been
much improved by any systems of art, or methodical institutions. The
logick, which for so many ages kept possession of the schools, has at
last been condemned as a mere art of wrangling, of very little use in
the pursuit of truth; and later writers have contented themselves with
giving an account of the operations of the mind, marking the various
stages of her progress, and giving some general rules for the regulation
of her conduct. The method of these writers is here followed; but
without a servile adherence to any, and with endeavours to make
improvements upon all. This work, however laborious, has yet been
fruitless, if there be truth in an observation very frequently made,
that logicians out of the school do not reason better than men
unassisted by those lights which their science is supposed to bestow. It
is not to be doubted but that logicians may be sometimes overborne by
their passions, or blinded by their prejudices; and that a man may
reason ill, as he may act ill, not because he does not know what is
right, but because he does not regard it; yet it is no more the fault of
his art that it does not direct him, when his attention is withdrawn
from it, than it is the defect of his sight that he misses his way, when
he shuts his eyes. Against this cause o