ascending and descending, throughout the day and night, will give a collateral estimate of a similar nature. The best practical mode of deducing this range from the observations is, to find separately the mean of the heights for the morning and afternoon, and to double their difference. Where none of these particulars can be obtained, the extreme variation of each month will afford a character not altogether unimportant. Mean of the greatest Variations of successive Days in each Month, for the Winter Months. London, 1790–4, 6 mo. Knightsbridge, Read, 1790-1 (greatest 23°) London, 1794 (greatest of all 15°) Dawlish, 1794 (greatest 131°) Lisbon, 1788 (greatest 11°) Bermudas, 1790 (greatest 13°) 11.59 Montreal, 1788 - 9.2 10.9 13.0 13.5 16. 11. Penzance, 1808-9. Nov. to March (gr. 10°)---- Sidmouth, 1800. Jan. to March (gr. 16°). Gravesend, 1787. Jan. Clifton, Feb. 1803, 9°, March, 13°, mean------- Mean Variation of successive Days for the Winter Months. London, 1790-4, 6 mo. London, 1794 Dawlish, 1794 Knightsbridge, 1790-1 5.45 3.68 Clifton, 1808. Feb. and March (Lond. 16.2°) Clifton, 1803. Feb. and March (Lond. 36°)------ 31° It does not appear that. Devonshire possesses any decided advantages over London with respect to equability of climate, if we judge of the climate of London from the observations made at the apartments of the Royal Society only: but in so central a situation, the changes must be rendered much less sensible by the effect of the surrounding buildings; and they appear to be considerably greater at Gravesend, and greater still at Knightsbridge. In this respect, too, Penzance retains its superiority even over Devonshire. Lisbon seems to have a less variable temperature than any part of Great Britain; and in Madeira, to judge by the monthly variation only, the advantage in this respect appears to be still greater. The greatest possible equability of temperature seems however to be obtained in a sea voyage to a warm climate, in which the variation seldom amounts to half as much as in the most favorable situation on shore, even on a small island; and in pulmonary cases the motion of a ship would probably, in general, be rather beneficial than otherwise, while the fatigue of travelling in bad roads, and the danger of sleeping in damp beds, present an alternative by no means favorable to a journey by land. The direction of the wind alone can seldom have any immediate effect on the salubrity of the climate, except by variously modifying its temperature, according to the seas or countries over which it blows. There is a method of computing the mean direction of the wind, which does not appear to have been hitherto adopted, but which affords a very simple and intelligible result, although somewhat laborious if extensively applied. It consists in finding the bearing and distance of a point, to which a light body would be carried by the wind in the course of the year, supposing the velocity to be constant, when its variations have not been ascertained by observation. It is obvious that the bearing of such a point will show at once the mean direction of the prevalent winds; and its distance, compared with the effect of a constant wind for the same time, as a unit, will indicate the degree in which those winds have prevailed. W. 6° S. 466. Dawlish, 1794 According to this comparison, it appears that the mean direction of the wind in Devonshire is somewhat more westerly than in London: and that the degree, in which such westerly westerly winds predominate, is more than twice as great as in London; or, if we convert the measure into days, that the predominance amounted, in 1794, to 68 days for London, of a wind nearly W. S.W. and to 170 days for Dawlish, of a wind a little to the south of west. The variations of the climate of the same place, with respect to mean temperature, are easily collected from the usual meteorological computations. Dr. Heberden has very successfully combated the common opinion respecting the superior salubrity of cold winters; it appears, however, that the winter which he particularly observed was more variable, as well as colder, than usual. Mr. Kirwan has attempted to account for the greater frequency of colds, which he supposes to occur in spring and in autumn, by the greater variability of the temperature at those seasons: but both the fact and the explanation are very questionable; for in reality the variations of temperature, if estimated by the total range of the thermometer within the 24 hours, are almost uniformly greatest in the hottest weather. In London, the greatest variations of successive days at the same hours in the morning are greatest in winter; in the afternoon, in summer; and, although the latter are a little greater in April than in some of the succeeding months, the difference is by no means considerable. } 451 Of the empirical evidence, which may be collected, respecting the medical effects of different climates, the most authentic is perhaps that which is derived from well-regu lated bills of mortality; since these documents ought to afford us a tolerable criterion of the general healthiness or unhealthiness of a place, from the proportion between the annual deaths and the population, and at the same time a pretty correct determination of the degrees in which different diseases are fatal. Thus, when we find that in Stockholm the annual deaths amount to of the population, in London to, in the Pays de Vaud to and in some villages in different parts of Great Britain to only, we cannot hesitate to consider a residence in the country as generally more healthy, than in a metropolis similar to either of those cities; although it cannot fairly be concluded that the healthiness is precisely in the proportion which might be inferred from this comparison, until we have considered how far the effect of emigration to a great town may influence the apparent mortality. After the age of eight or ten, the probable duration of life may be estimated with sufficient accuracy, as Demoivre has very ingeniously shown, by assuming that, of a certain number of persons born together, one will die annually until the whole number is be come come extinct; and it is well known, that this number may in common cases be supposed to be 86; so that at any given age, for instance 36, we may find the probable duration of life by deducting it from 86, and halving the remainder, which will give us 25 for the estimate required; and if this law were universally true from the time of birth, it is easy to show that the mortality in a metropolis would always be increased by the accession of settlers; so that if, for example, the whole population were supplied by settlers at 20, and all children were sent to a neighbouring village to be educated, the mortality of the town, instead of, would become 1: (43—10) , and that of the village would be 1: (86-10) = ✈ ; and that any partial changes of a similar nature would cause a smaller alteration of the apparent salubrity, in proportion to their extent. But the mortality during infancy is actually much greater than is assumed in the simple hypothesis of Demoivre; and from this circumstance, as well as from the frequent return of aged persons into the country, Dr. Price has inferred that emigration in general has no tendency to increase the mortality of cities. In reality, the question depends altogether upon the mortality which may be supposed to take place within the first year, which is often estimated at one-third of the births; but nothing like this can well be expected to occur at any tolerably healthy place in the country; and on the whole it does not appear that Dr. Price's observations can by any means be admitted as conclusive. With respect to the evidence afforded by the prevalence of diseases, it has been observed by Dr. Gregory, that removing from a colder to a warmer climate may be beneficial, even in those diseases to which the inhabitants of the warmer climate are subject; but if they appeared to be equally or more subject to any disease than the inhabitants of the colder, there would surely be little encouragement for the change: for instance, in a person supposed to be liable to diseases of the liver, it would surely be injudicious to undertake a voyage to a hot climate, with a view of avoiding the chance of taking cold, since the wellknown frequency of hepatitis, in such climates, would much more than counterbalance any prospect of advantage from the change. The frequency of consumptions is decidedly greater in cold than in hot climates, but not by any means in exact proportion to the depression of the mean temperature. The principal situations, that require to be compared with the metropolis, as a standard, are the south of England, the south of Europe, the islands of the Mediterranean, Madeira, and the West Indies. There There do not appear to be any precise accounts of the proportionate mortality from consumption at any place upon the southern coasts of this island, on a scale sufficiently extensive for the comparison; but there is abundant reason to think that such a report would be greatly in favor of the salubrity of these coasts, more so indeed than any conclusions, that we should be at all authorised to form, from such thermometrical observations as have hitherto been compared. A greater number of registers is still wanting to obtain sufficient evidence for the inquiry: and it would be desirable that some journal should be kept at one of the Scilly islands, as a situation fully exposed to the influence of the sea air; for there can be little doubt that, for equability of temperature, a very small island must have great advantages above every other situation on shore. But in the present state of our knowledge on this subject, although we are fully justified in recommending a residence in Devonshire or Cornwall as advisable in a certain stage of consumption, it does not appear that any meteorological observations will authorise us to represent the advantages to be gained by such a residence, as by any means equivalent to those which may be found in remoter situations; nor that the empirical testimony, derived from accounts of the comparative prevalence of the disease, is at all so clear, or so firmly established, as to make up for the want of evidence of a great and decided superiority of the climate. In the south of Europe, the situations which have been most frequented are Lisbon, or some other part of the peninsula, the neighbourhood of Montpelier, and different parts of Italy. In Spain, and probably in Portugal, consumption is said to be not common, but by no means wholly unknown; and whether from accident, or from causes which are likely to have a constant operation, the climate of Portugal has certainly failed, in a number of instances, of producing any material benefit, where there has been apparently fair chance for the patient's recovery. With respect to the south of France, it is perhaps sufficient to remark, that the general proportion of deaths from consumption at a very served in London, where, according to Dr. Heberden's remark, its prevalence has of late years been so much increased. In Italy the disease appears to be decidedly less frequent; and there is no reason to doubt but that, in the southern parts of that country, there may be situations approaching in their dimates to those of the neighbouring islands. It is, however, highly probable that some of these islands. possess very considerable advantages over almost every part NO. 174. T of |