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

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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 in superseding the necessity