18 Mr. T. Pt. Edmonds on Vital Force according 



with a combustible, but the rearrangement of the elementary 

 constituents of a complex molecule in a state which, for want of 

 a better term, I have called elsewhere* " chemical tension." In 

 the communication alluded to the evolution of nerve-force only 

 was considered, and the conclusion here stated was reached de- 

 ductively, but experimental confirmation is afforded by Hermann's 

 researches on the chemical changes attending muscular action. 



III. OnVitalForce according to Age, and the "English Life Table" 

 By Thomas Rowe Edmonds, B.A. Cantab.f 



OBSERVATIONS on the vital force of man at different ages 

 from birth are all of modern date. The idea of the exist- 

 ence in every population of a law of vital force according to age 

 was not entertained by mankind until near the end of the seven- 

 teenth century. The embodiment of this idea in a " Table of 

 Mortality " was first made about the year 1693, by our country- 

 man, Dr. Halley. The form of the Table of mortality adopted 

 about the year 1738, and continued in use to the present time, 

 may be described as follows : — Such Table consists of three co- 

 lumns. The heading of the first column is " Age/' of the se- 

 cond column u Living," and of the third column " Dying." The 

 numbers in the first column denote completed years of age from 

 birth-time, beginning at age and ending, say, at 99 years. 

 The numbers in the second column denote the living or survi- 

 vors at any completed year of age out of a given number born or 

 living at the age 0. Lastly, the numbers in the third column 

 denote the numbers dying during the year of age next following 

 the completed year marked, in the same horizontal line, in the 

 first column. 



In a Table of mortality, if the numbers in the column of 

 "Living " be represented by the letter P, the numbers in the 

 column of "Dying " will be represented by AP, for a unit of 

 time or age taken to be one year. If the time or age be reckoned 



AP 



from birth, we shall have at any age t the quantity -t— -to re- 



present the ratio of the numbers dying during the (t+ l)th year 

 of age to the numbers living at the beginning of the same year 

 of age. If the intervals of age, instead of being each one year, 

 be diminished indefinitely, we shall have to substitute the differ- 

 ential of P* or d . P^ for AP^ 'in the above ratio. We shall then 



d. P 

 obtain ' .* , or d . log e Pj* for the expression of the ratio of the 



* Proceedings of the lloyal Society, June 1868. 

 f Communcated by the Author. 



