JrxESl, 1895.] 



SCIENCE. 



685 



of tlie State lias involved a careful study of 

 the relation lietween precipitation and 

 stream flow. Tliis study has led to some 

 very important conclusions, the data for 

 which are drawn not merely from within the 

 State of Xew Jersey, but from all available 

 sources. The analysis of tlie facts has led 

 Mr. Yermeule to the conclusion that a for- 

 mula may be adopted which shall express 

 ■with approximate accuracy the relation l)e- 

 tween rainfall and evaporation, within the 

 basins of the streams studied. This formula 

 is E=15.o0-r.lt? K. in which E= total an- 

 nual evaporation, R^ annual precipitation, 

 and 15.50 stand for inches of vater. R 

 minus E will equal the annual flow of the 

 river in question. A modification of the 

 formula for mean annual temperature is 

 suggested, and in this modified form it 

 becomes universal. In this connection it 

 is stated that a careful study of the annual 

 precipitation and flow of variously widely 

 separated streams " has practically demon- 

 strated that the diflerence iu amount dis- 

 charged (by streams) for given rainfalls is 

 due almost entirely to increase or decrease 

 of evaporation owing to increased or de- 

 creased annual temperature " (p. 75); and 

 that temperature is ' a much more potent 

 factor than forests, topography, or the other 

 causes usuallj' assigned " (p. 77) to account 

 for the variations in the discharges of 

 streams. So thoroughly is evaporation be- 

 lieved to be dependent on temperature that 

 "the (river) gaugings (representing the 

 rainfall which does not evaporate) actually 

 indicate the mean temperature of the water 

 sheds more closely than we can obtain it 

 from available temperature observations" 

 (p. 334). It will be readily seen that the 

 formula} noted above, and the principles 

 which go along with them, greatly simplify 

 the whole ((uestiou of the relation of rain- 

 fall and stream flow, and are of the 

 greatest importance to all interests dejiend- 

 ent on streams, or effected by them. For- 



nuihe are deduced for calculating the propor- 

 tion of rainfall which disapi>ears by eva- 

 poration for each month, and for determin- 

 ing the flow of a stream for any given 

 month, the i-aiufall and temperature of its 

 basin being known. 



Of immediate practical value to the citi- 

 zens of the State are the detailed data con- 

 cerning the streams of New Jer.sey. These 

 data include the total, the average and the 

 minimum flow of each stream of the state, 

 the available and the utilized power, etc., 

 etc. The data are combined in various 

 ways with a view to making them usefal 

 in various directions. 



Popular ideas to the contrary notwith- 

 standing, statistics show that there has 

 been a slow but steady increase in the use 

 of water power within the State. While 

 many small powers have been abandoned, 

 this loss has been made more than good by 

 the establishment of larger ones. The total 

 amount now in use is about 31,000 horse 

 power. Pertinent suggestions are offered 

 as to the further utilization of the power 

 afforded by the streams. 



Foi-ests are thought not to influence the 

 annual evaporation or stream flow to any 

 marked extent, nor to influence particu- 

 larly extreme floods. AVith deforesting, how- 

 ever, comes increased irregularity of stream 

 flow, including more frequent moderate 

 floods, lower flow of streams during periods 

 of drought, and more protracted periods of 

 low flow (page 344). Care is taken to em- 

 phasize the beneficial eftects of forests in 

 preserving soil on slopes, in creating absorb- 

 ent matter (humus, etc.), which holds the 

 water and helps to equalize its flow. 



Cultivation is thought not to greatly af- 

 fect the total stream flow, though it aflects 

 its regularity. It increases the absorbent 

 capacity of the soil, and so the total flow 

 from underground water, while under drain- 

 age tends to produce irregularity of flow. 

 "As between cultivated and barren water- 



