102 SEWER DESIGN 



This law and the discussion must be used with great caution 

 in the case of any particular city, the general law being often 

 very wide from the truth. From Table XIII it is seen that cities 

 of 10,000 inhabitants increased in population in 1900-1910 

 from o.o to 10.7 per cent per year, while the general law would 

 indicate about 1 1 per cent. Cities of 30,000, however, apparently 

 may, as a maximum, increase at the rate of 23 per cent. Should 

 the city in question not be an average city, a large error would 

 evidently result from trying to apply the general law. 



No law or estimate can be found for new cities such as 

 spring up in the western part of the United States. There 

 may be cited as an example San Diego, which, in January, 

 1887, when the plans were made for its sewer system, had a 

 population of 5000. In February, 1888, there was a population 

 of 33,000, and by the Census of 1890 the town had a population 

 of 16,129. I n 1910 the population was 39,578. 



To further illustrate the method of securing an idea of the 

 future population, Fig. 23 is given from a thesis on the sewerage 

 of Ithaca, by Mr. W. E. Truesdell, C.E., Cornell University, 

 1896. The city population of Ithaca was given by U. S. Census 

 for 1880 and 1890, and there was also available an unofficial 

 census in 1892 which did not, however, check with the other 

 two. The following additional records were consulted and 

 plotted on the same diagram as the Census figures: the maximum 

 vote in city elections for every five years from 1855 to 1897; 

 the yearly public-school registration from 1879 to 1897; tne 

 school population from 1871 to 1891. The rate of increas- 

 of the population of the city was taken as the mean of the 

 rates of increase in votes, in school registration, in school popula- 

 tion, and in the Census reports, weighting the different records 

 as the peculiar condition seemed to justify. In the figure, 

 the long broken line shows the apparent increase as indicated 

 by the local censuses, while the long heavy line shows the 

 adopted line, modified by the two government censuses of 1880- 

 1890. By Kuichling's method the population in 1920 will 

 be 113,000, while by Mr. Truesdell's it will be only 18,500. 



