250 



BIOLOGY OF DEATH 



kind of problem that confronts the astronomer calculat- 

 ing the complete orbit of a comet. The astronomer never 

 has more than a relatively few observations of the posi- 



3 



g 113 



5 » 



Fig. 61. — ShowinE the curve of growth of the population of the United States. For further 

 explanation of this and the two following diagrams, see text. 



tion of the comet. He has, from Newtonian principles, 

 a general mathematical expression of the laws of motion 

 of heavenly bodies. He must then construct his whole 

 curve from the data given by the few observations. So, 

 similarly, the statistician has but a relatively few popu- 

 lation observations because census taking has been prac- 

 tised along present lines only a little more than a century. 

 According to the stage in historical development of the 

 country dealt with, he may have given an early, a late, or 

 a middle short piece of the population "orbit" or his- 

 tory. From this he must construct, on the basis of his 

 general theory of "population orbits," the whole history, 

 past and future, of the population in question. 



To demonstrate how successful the population curve 

 shown in Figure 60 is in doing this, three diagrams are 

 presented, each illustrating the growth of the population 



