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. 'Tis 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. 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; 'tis 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 'tis 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.