SCIENCE 



Feidat, December 15, 1911 



CONTENTS 

 Principles of Water-power Development: Dr. 

 W J McGee 813 



University Extension, and the State Univer- 

 sity: Professor Louis E. Eeber 825 



An Opportunity for the Spirit of Besearch 

 in Laboratory Instruction in Physics: Pro- 

 PESSOE G. W. Stewart 833 



A New Gas Volcano in Trindad: Egbert An- 

 derson 834 



The Future of the London Zoological Gardens 835 



Scientific Notes and News 836 



University and Educational News 840 



Discussion and Correspondence : — • 



"Genotype" and "Pure Line" : Professor 

 H. S. Jennings. Mosquito Romance: 

 KONOPS. Bow a Falling Cat turns over in 

 the Air, How to throw a Curved Ball: Pro- 

 fessor W. S. Franklin. Seed Distribution 

 by Surface Tension: Henry S. Conard. 

 Models of Vorticella and Cyclops: Pro- 

 fessor Henry P. Nachtrieb. Siphon 

 Springs and Sinh Holes: Professor H. F. 

 Cleland. The Mole of Salts in the Preser- 

 vation of Life: Professor Jacques Loeb . 84] 



Scientific BooTcs: — 



Observations and Investigations made at 

 the Blue Hill Observatory: Professor E. 

 Dec. Ward. Iddings's Bock Minerals: 

 Dr. Geo. P. Merrill. Alder and HancocTc 

 on British Nudibranchiate Mollusca; Ant- 

 arctic Expedition of the DuTce of Orleans: 

 Dr. Wm. H. Dall. Newbigi/n's Modern 

 Geography: Professor Eichard W. Dodge 846 



The Convocation Week Meetings of Scientific 

 Societies 851 



MSS. intended fot publication and booka, etc., intended for 

 MTiew should be sent to the Editor of Science, Garrison-on- 

 Hudson, N. Y, 



PEINCIPLES OF WATEB-POWEB 

 DEVELOPMENT ' 



1. The development of water-power in- 

 volves artificial regulation of streams. 

 Proper regulation of running water for 

 the several uses of water supply, irriga- 

 tion, power and navigation can be effected 

 only in the light of the physical relations, 

 the relations in equity, and the more salient 

 legal relations of water in streams. 



PHYSICAL RELATIONS 



2. The fresh water of the land is de- 

 rived directly from rainfall (including 

 snow) and indirectly through evaporation 

 from the sea. The mean annual rainfall 

 on mainland United States ranges from 

 less than 5 to over 100 inches, averaging 30 

 inches; the quantity aggregates about 

 5,000,000,000 acre-feet.2 The distribution 

 is unequal; over the eastward two fifths of 

 the country^ the mean is about 48 inches, 

 over the median fifth some 30 inches, and 

 over the westward two fifths about 12 

 inches.' 



3. In humid lands the water of rains 

 and melting snows tends to gather into 

 streams, generally taking the shortest and 

 easiest paths to the sea, while in arid lands 



' Presented at a hearing of the National Water- 

 ways Commission, November 21, 1911. 



- The acre-foot is a convenient unit not only 

 because in common use throughout arid America, 

 but because large enough" to measure water in its 

 national aspect without use of incomprehensibly 

 large figures. It equals 43,560 cubic feet, 326,047 

 gallons, or 1,359.6 tons; it is something over a 

 kilostere (equaling 1.2335 ks.), or cube of 10 

 meters. 



= "Soil Erosion," Bureau of Soils Bulletin 71, 

 1911, p. 17. 



