Were they convinced, that their discoveries were of no consequence, they would entirely lose all relish for their studies, and that though the consequences be entirely indifferent to them; which seems to be a contradiction.
To remove this contradiction, we must consider, that there are certain desires and inclinations, which go no farther than the imagination, and are rather the faint shadows and images of passions, than any real affections.

Thus, suppose a man, who takes a survey of the fortifications of any city; considers their strength and advantages, natural or acquired; observes the disposition and contrivance of the bastions, ramparts, mines, and other military works; it is plain, that in proportion as all these are fitted to attain their ends he will receive a suitable pleasure and satisfaction.

This pleasure, as it arises from the utility, not the form of the objects, can be no other than a sympathy with the inhabitants, for whose security all this art is employed; though it is possible, that this person, as a stranger or an enemy, may in his heart have no kindness for them, or may even entertain a hatred against them.
It may indeed be objected, that such a remote sympathy is a very slight foundation for a passion, and that so much industry and application, as we frequently observe in philosophers, can never be derived from so inconsiderable an original.

But here I return to what I have already remarked, that the pleasure of study conflicts chiefly in the action of the mind, and the exercise of the genius and understanding in the discovery or comprehension of any truth.

If the importance of the truth be requisite to compleat the pleasure, it is not on account of any considerable addition, which of itself it brings to our enjoyment, but only because it is, in some measure, requisite to fix our attention.
When we are careless and inattentive, the same action of the understanding has no effect upon us, nor is able to convey any of that satisfaction, which arises from it, when we are in another disposition.
But beside the action of the mind, which is the principal foundation of the pleasure, there is likewise required a degree of success in the attainment of the end, or the discovery of that truth we examine.