and the Intemity of Hiimmi Life. 201 



into a detail of the enormous miscalculations which have 

 thence arisen*. 



With reference to each year of age, either the fraction 

 which measures the probability that life will endure another 

 year, or else the corresponding quantity of living persons, out 

 of which one death (precisely) is to occur during the same in- 

 terval, will constitute two modes equally eligible of expressing 

 the intensity of life from year to year. In both sexes, this in- 

 tensity is less at the birth* than at any intermediate period from 

 that time, until an advanced age attainable only for the pri- 

 vileged few ; but it gradually increases, so long as the human 

 frame acquires any further development, and whilst nature 

 may continue its supply of additional vigour, provided that no 

 counteracting causes enter into operation ; and from the period 

 at which such intensity has arrived at a maximum, it invariably 

 decreases, but in modified progressions, until all probability of 

 life's continuance becomes extinct, as far as considered in each 

 individual. At the same time this constant decrease has its 

 period of limitation, with reference to any considerable num- 

 ber of lives of the same class, and taken together j which oc- 

 curs in the following manner : — 



At a certain age, which may vary from the eighty-third to the 

 ninetieth year, according to the description of a whole popu- 

 lation or any select portion of it, an anomaly is exhibited in 

 the shape of apparent increase, as to the intensity of life, du- 

 ring a few years. Not that individual lives have actually im- 

 proved; but considered in the aggregate, such as were ori- 

 ginally constituted for outliving their cotemporaries, and who 

 continued to exist under the most favourable circumstances, 

 ultimately stand prominent, competing amongst themselves 

 for protracted longevity, to the exclusion of all the rest. In- 

 deed, this natural selection of particular lives, out of a very 

 considerable mass, repeatedly occurs among centenaries, at 

 later periods, and according to their respective degrees of con- 

 stitutional vigour ; so that very little difference may appear in 

 the probabilities of living one more year, between two indivi- 

 duals of whom the ages differed even to the extent of twenty 

 years. By duly attending to this consideration, a law of morta- 

 lity may be so constructed as to represent, with all possible ac- 

 curacy, the progressive expenditure of human life to the utmost 

 attainable age, and without such statement being ever at vari- 

 ance with recorded facts of longevity, however extraordinary. 



• After analysing all the laws of mortality set forth to the present time, 

 critical remarks upon them, and other matter connected with this subject, 

 have been given in the" Atlas," of the 6th, 20th, and 27th of April, 4th 

 and 20th of May, 1828. 



N. S. Vol. r,. No. 27. Marr/i 1829. 2 D When 



