850 On the probable Dtiratiort of Human Life. 



bailee, than from any great revolution in the currents of the 

 atmosphere. Upon the land they might be produced by local 

 circumstances, such as a heated space of ground, which would 

 force the current upwards ; and he could imagine water-spouts 

 revolving in either one direction or the other. As to Mr Espy's 

 theory, though he considered it ingenious, yet he did not see 

 how it was tenable against the indications of the barometer. 



On the probable Duration of Human Life.* 



Dr Caspar of Berlin, in his valuable work, entitled ' Der 

 wahrscheinliche Lebensdaur des Menschen, &c.,' 1835, after 

 having examined the current opinions as to the average dura- 

 tion of human life, and as to the most satisfactory method of 

 ascertaining such a result, announces his own doctrine in the 

 following proposition: — The proportion of births to the popu- 

 lation in any place expresses almost exactly the medium or ave- 

 rage duration of life there. 



For example, suppose that this proportion is in the ratio of 

 1 to 28, th«i the average life of the inhabitants of the place 

 will be found to be 28 years. 



If this rule be correct, it must follow that the duration of 

 life increases and diminishes in a population, according as their 

 fecundity is greater or less ; so that man, if not as an indivi- 

 dual, at least as a member of the mass, may be said to have it 

 in his power to lengthen or to abridge his life. 



This, if true, is indeed a proposition of great importance in 

 political economy. 



To prove that the mortality is in a direct ratio with the fe- 

 cundity of any population, and, consequently, that govern- 

 ments, seeing that the force of states consists not so much on 

 the mere number, as on the strength, fecundity, and longevity 

 of their inhabitants, ought not to favour or encourage an over 

 abundant population, the author has collected together a vast 

 number of facts, and for this purpose has drawn up tables of 



* Medico-Cliirurgical Review, July 1838. 



