1917] 



EURAL ECONOMICS. 



591 



ing systems, his purpose being apparently to advance a step in standardization. 

 The systems are classified as follows: (1) Plants that give light only when the 

 generator and engine are running; (2) plants that give light only from the bat- 

 tery, tl'.e generator being used only for charging the battery; (3) plants that 

 give light from the battery or from the battery and generator combined; and 

 (4) plants that give light either from the battery or generator, or from both. 



The following general types coming under each class are suggested : Manual — 

 plants that are entirely manually started, operated, regulated, and stopped; 

 semiautomatic — plants that are partially automatic in some one or more features, 

 but not entirely so ; all automatic — plants that are entirely automatic in start- 

 ing, regulating the voltage and charging battery, automatically stopping when 

 the charge is complete or no lights are in use. 



With reference to voltage, it is stated that " 32 volts has become a standard 

 for small plants having lights in a small area; 115 volts is better if the dis- 

 tribution system covers a (on.sidcrable distance from the plant and if motors 

 other than small household motors are to be used." With reference to speed 

 of generator, it is stated that " if belt driven, 2.300 revolutions per minute or 

 less gives general satisfaction. If direct coimecled to the engine the speed 

 should be lower, perhaps 800 to 1,000 maximum, although experiments are con- 

 tinually being made to produce higher speed engines that are not noisy and hnve 

 a reasonable life." 



Sewage disposal for country homes, F. F. Frazieu (Kans. Agr. Col. IJxt. Bui. 

 6 {1916). pp. SO, figs. 6). — This bulletin describes and illustrates the design and 

 construction of small sewage disposal systems consisting of sei)tic tanks and 

 tile absorption areas. The author lays more stre.-ss on the chemical and bac- 

 teriological phases of sewage purification than has been the custom in previous 

 reports by others on the sub.lect, and his reconunendations indicate that some 

 study along that line has been made. 



RIJE.AL ECOI^OMICS. 



[A study in social dynamics], J. M. Oilt.ette {Quart. Piihs. Amcr. Statis. 

 Assoc, n. ser.. 15 {1916), No. 116, pp. 345-3S0, figs. 2).— The author lias en- 

 deavored to determine statistically the rate of natural increase and the factors 

 accounting for the increase in the rural and urban population of the United 

 States. He describes in detail the method used and the results obtained. The 

 natural increases as determined by his method are shown in the following table : 



Rates of birth, death, and natural increase in the United States for the deeade 



1900-1910. 



