people of food, according as he discovered the moon's age by the almanack. To ascertain how far this opinion was founded in fact, I kept, during more than two years, an exact register, but without finding, in any instance, that the aberrations of the human intellect corresponded with, or were influenced by, the vicissitudes of this luminary. As insane persons, especially those in a furious state, are but little disposed to sleep, even under the most favourable circumstances, they will be still less so, when the moon shines brightly into their apartments. It has also been considered, that intellectual labour frequently becomes a cause of insanity; that those, who are in the habit of exercising the faculty of thought, for the perfection and preservation of the reason of others, are thereby in danger of losing their own. We hear much of this, from those who have copiously treated of this disease, without the toil of practical remark; whose heads become bewildered by the gentlest exercise, and to whom the recreation of thinking becomes the exciting cause of stupidity or delirium. These persons enumerate, among the exciting causes of delirium, "Too great, or too long continued exertion of the mental faculties, as in the delirium which often succeeds long continued and abstract calculation; and the deliria to which men of genius are peculiarly subject." The mind of every man is capable of a definite quantity of exertion to good effect; all endeavours, beyond that point, are impotent and perplexing. The attention is capable of being fixed to a certain extent, and, when that begins to deviate, all continuance is time lost. It is certain that, by habit, this power may be much increased; and, by frequent exercise, that, which at first excited fatigue, may be continued with facility and pleasure. What species of delirium is that, which succeeds long continued and abstract calculation? Newton lived to the age of 85 years, Leibnitz to 70, and Euler to a more advanced period, yet their several biographers have neglected to inform us, that their studies were checquered with delirious fermentations. The mathematicians of the present day (and there are many of distinguished eminence) would conceive it no compliment to suppose that they retired from their labours with addled brains, and that writers of books on insanity should impute to them miseries which they never experienced. It is curious to remark, in looking over a biographical chart, that mathematicians and natural philosophers have in general attained a considerable age; so that long continued and abstract calculation, or correct thinking upon any subject does not appear, with all these delirious visitations, to shorten the duration of human life. What is meant by the deliria, to which men of genius are peculiarly subject, I am unable, from a want of sufficient genius and delirium, to comprehend.