25S ^n Essay on the medical Effects of Climates. 



born together, one will die annually until the whole num- 

 ber is become extinct; and it is well known, that this 

 number may in common cases be supposed to be 8G ; so 

 that at any given age, for instance 36, we may find the 

 probable duration of lite by dtducling it from 86, and 

 halving ihe remainder, which will give us CA for the esti- 

 mate required ; and if this law were universally true from 

 ihe time of birih, it is easy to show that the mortality in a 

 metropolis would always be increased by the accession of 

 settlers ; so that if, for exan)ple, 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 I : (43 — 10) = -3-'-) and 

 that of the village would be 1 : (86—10) = y^; 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 snnple 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 enii(;ration in general has no tendency to 

 increase the mortality of cities. In reality, the question de- 

 pends 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 anv means be admitted as con- 

 clusive. With respect to the evidence afforded by the pre- 

 valence of diseases, it has been observed by Dr. Gregory, 

 that removing from a colder to a warmer climate may lie 

 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 inhabi- 

 tants of the colder, there would surely be little encourage- 

 ment for the change: for instance, in a person supposed 

 to be liable to diseases of the liver, it would surely be in- 

 judicious to undertake a voyage to a hot climate, with a 

 view ot" avoiding the chance of taking cold, since the well 

 known frequency lif hepatitis, in such climates, would 

 much more ihan counlerbalauce any prospect of advantage 

 from the change. 



The frequency of consumptions is decidedly greater in 

 cold than in hot climates, hut 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. 



