Page:An Essay on the Principle of Population (1798).djvu/262

 has given us some little insight into these causes, and has therefore enabled us better to judge, if not, of what we are to expect in future, at least, of what we are not to expect, which, though negative, is a very useful piece of information.

As the necessity of sleep seems rather to depend upon the body than the mind, it does not appear how the improvement of the mind can tend very greatly to supersede this "conspicuous infirmity." A man who by great excitements on his mind, is able to pass two or three nights without sleep, proportionably exhausts the vigour of his body: and this diminution of health and strength, will soon disturb the operations of his understanding; so that by these great efforts, he appears to have made no real progress whatever,