No. G41] 



THE DURATION OF LIFE 



493 



The plan of arrangement of Tables II to V is as fol- 

 lows : The first column gives the age of the flies in days, 

 starting theoretically from the time of the emergence of 

 the imago from the pupa as zero. Since the flies spend 

 on the average a day in the breeding bottle before they 

 are taken out into the small duration-of-life bottles, and 

 the deaths are not observed for this interval, our distri- 

 butions as recorded actually start with age 1 instead of 

 age 0. The next two columns give the observed deaths 

 and survivors on the basis of a thousand individuals at 

 ''birth" (here emergence as imago). The next three 

 columns give the calculated (graduated) values deduced 

 from equations (ii) to (v) above; first the U line, next 

 the q^, and finally the ex, the latter values being of course 

 in days. Owing to the fact that no premium rates are 

 likely to be calculated from these life tables, we have not 

 thought it necessary to keep but one place of decimals in 

 the case of the qx and ex lines, and none whatever in the 

 Ix line. Of course, in the computations more decimal 

 places were kept, and these life tables may be regarded as 

 accurate to a considerably higher degree than the figures 

 as here published indicate. But, on the other hand, so 

 far as we can see, the figues here tabled are sufficiently 

 detailed for any use to which they are ever likely to be 

 put. 



The Ix lines of Tables II to V are s1io\\ti graphically in 

 Figs. 1 and 2. The diagrams are plotted to an arithlog 

 grid, the scale of the abscissa being divided arithmet- 

 ically, and that of the ordinates logarithmically. Field 

 (24) has sho^\^l the advantages of this method of plotting 

 life table L lines. He says: 



