‘Variations from different causes are essentially distinct from a regular and unretrograde increase. The average duration of human life will, to a certain degree, vary, from healthy or unhealthy climates, from wholesome or unwholesome food, from virtuous or vicious manners, and other causes; but it may be fairly doubted, whether there has been really the smallest perceptible advance in the natural duration of human life, since first we had any authentic history of man. The prejudices of all ages have, indeed, been directly contrary to this supposition.’ Now this statement is very unsatisfactory, to say the least. For the only reason that can be given why the causes here mentioned, on which Mr. M. allows that the duration of human life depends, have not produced a regular and permanent effect _must be_, that they themselves have neither been regular nor permanent. The mere fact, therefore, of the variableness in the length of human life proves nothing but the variableness of those moral and artificial causes, which are supposed to have some influence on our physical constitution. But Condorcet supposes a regular advance to be made in these causes, and that an indefinite advance in some of them (as the knowledge of medicine for instance) is probable, will hardly be disputed. The question (in this point of view) of the necessary duration of human life is not properly a question of fact, or history, but depends on a comparison of the present circumstances of mankind with their past circumstances, and on the probability that may thence appear of preventing or counteracting those maladies and passions which are most unfavourable to long life. That our reason may sometimes get the start of our experience is what no one can deny. Thus when the art of printing was first discovered it required no great stretch of thought to perceive that knowledge and learning would soon become more generally diffused than they had hitherto been, though till this event no perceptible or regular progress had ever been made. Those who reason otherwise are a kind of stereographic reasoners who take things in the lump without being able to analyse or connect their different principles. Experience is but the alphabet of reason. With respect to the general shortness of human life compared with what it was in the first ages of mankind, this fact seems rather against Mr. Malthus, for if there is no certain date, no settled period to human life, beyond which it cannot hold out, but that it has varied from a thousand to a hundred years, so far there is no reason why we should not tread back our steps, or even go beyond the point from which we set out. There is no fixed limit; the present length of human life is not evidently a general law of nature. The mere naked fact of its never exceeding a certain length at present is just as decisive against its ever having been longer, as it is against its ever being longer in future. Mr.