We love to trace the demonstrations of mathematicians; but should receive small entertainment from a person, who should barely inform us of the proportions of lines and angles, though we reposed the utmost confidence both in his judgment and veracity.

In this case it is sufficient to have ears to learn the truth.
We never are obliged to fix our attention or exert our genius; which of all other exercises of the mind is the most pleasant and agreeable.
But though the exercise of genius be the principal source of that satisfaction we receive from the sciences, yet I doubt, if it be alone sufficient to give us any considerable enjoyment.

The truth we discover must also be of some importance.

It is easy to multiply algebraical problems to infinity, nor is there any end in the discovery of the proportions of conic sections; though few mathematicians take any pleasure in these researches, but turn their thoughts to what is more useful and important.

Now the question is, after what manner this utility and importance operate upon us?
The difficulty on this head arises from hence, that many philosophers have consumed their time, have destroyed their health, and neglected their fortune, in the search of such truths, as they esteemed important and useful to the world, though it appeared from their whole conduct and behaviour, that they were not endowed with any share of public spirit, nor had any concern for the interests of mankind.