ll talk to most unintelligibly, and to all unpleasantly.

I was once present at the lectures of a profound philosopher, a man
really skilled in the science which he professed, who having occasion to
explain the terms _opacum_ and _pellucidum_, told us, after some
hesitation, that _opacum_ was, as one might say, _opake_, and that
_pellucidum_ signified _pellucid_. Such was the dexterity with which
this learned reader facilitated to his auditors the intricacies of
science; and so true is it, that a man may know what he cannot teach.

Boerhaave complains, that the writers who have treated of chymistry
before him, are useless to the greater part of students, because they
presuppose their readers to have such degrees of skill as are not often
to be found. Into the same errour are all men apt to fall, who have
familiarized any subject to themselves in solitude: they discourse, as
if they thought every other man had been employed in the same inquiries;
and expect that short hints and obscure allusions will produce in others
the same train of ideas which they excite in themselves.

Nor is this the only inconvenience which the man of study suffers from a
recluse life. When he meets with an opinion that pleases him, he catches
it up with eagerness; looks only after such arguments as tend to his
confirmation; or spares himself the trouble of discussion, and adopts it
with very little proof; indulges it long without suspicion, and in time
unites it to the general body of his knowledge, and treasures it up
among incontestable truths: but when he comes into the world among men
who, arguing upon dissimilar principles, have been led to different
conclusions, and being placed in various situations, view the same
object on many sides; he finds his darling position attacked, and
himself in no condition to defend it: having thought always in one
train, he is in the state of a man who having fenced always with the
same master, is perplexed and amazed by a new posture of his antagonist;
he is entangled in unexpected difficulties, he is harassed by sudden
objections, he is unprovided with solutions or replies; his surprise
impedes his natural powers of reasoning, his thoughts are scattered and
confounded, and he gratifies the pride of airy petulance with an easy
victory.

It is difficult to imagine, with what obstinacy truths which one mind
perceives almost by intuition, will be rejected by another; and how many
artifices must be practis