88 LIGHT SCIENCE FOR LEISURE HOURS. 



successive weeks, have indicated a law of increase, 

 which is very readily expressed so as to accord with 

 the mortality during those weeks, and perhaps two or 

 three following weeks. But if such a law were ex- 

 tended indefinitely it might be found to imply nothing 

 short of the complete .desolation of the country by 

 cholera, within the space of a few months. Thus, if the 

 deaths (from cholera) in five successive weeks were 20, 

 27, 35, 47, and 63, numbers corresponding with the 

 general characteristics of cholera mortality in the earlier 

 stages of a visitation, the weekly mortality a year 

 later, estimated according to the observed percentage 

 of increase, would be more than 173 millions! Now 

 this method of estimation, though leading to this pre- 

 posterous conclusion as respects a more distant epoch, 

 would probably lead to tolerably correct results for the 

 next week or two after that in which 63 persons died, 

 the estimated numbers being 84 and 110 for the next 

 two weeks respectively. 



It seems to me, therefore, that we are not justified, 

 by the observed seeming fulfilment of Mr. Jevons's 

 anticipations, in concluding that a hundred years hence 

 the consumption of coals will be 2,000 millions of tons, 

 or that the total consumption during the next 110 years 

 will be 100,000 millions of tons. We might almost as 

 safely infer that because a growing lad requires such 

 and such an increase of food year by year, the grown 

 man will need a similar rate of increase, and the 

 septuagenarian require so many tons and hogsheads 

 of solid and liquid food per diem. 



