June 9, 1910] 



SCIENCE 



821 



by the application of force. Anything that 

 has these qualities is called " matter," hence 

 the definition of matter. Lift the stone. The 

 lifting requires the application of force. 

 Force, a push or a pull. Resistance, a force 

 which acts opposite to the lifting force, the 

 force of gravity in this case. The stone 

 weighs 10 pounds, it is lifted 5 feet against a 

 resistance of 10 pounds. The operation of 

 lifting or of overcoming the resistance through 

 a distance is called work. Work is defined as 

 the exertion of force or the overcoming of 

 resistance through space, and is measured as 

 the product of the force and the distance. The 

 product of 10 pounds and 5 feet is 50 foot- 

 pounds of work. Let the stone fall. Gravity is 

 now the applied force and there is no opposing 

 resistance (neglecting the slight air-resistance) 

 until the stone reaches the earth. It acquires 

 speed during the fall, the speed increasing at 

 the rate of 32.2 feet per second in each second, 

 and when it has falle n 5 feet it has attained 

 a velocity Y = \/2gh = 17.9 ft. per sec. 



Thus the student is led forward from the 

 simple concepts which he already has, say at 

 the age of 12 years, as clear as he will ever 

 have them throughout his life, of solid, liquid, 

 gas, distance, force, time, to the meaning of 

 the general term " matter " and to the com- 

 pound concepts work and velocity, and he is 

 now prepared to go a step further and meet 

 the words, stored work, energy, potential and 

 kinetic, energy of motion, mechanical energy, 

 and to understand the definition: Energy, or 

 stored work, the capacity for performing work. 



This definition is pedagogically sound, scien- 

 tifically accurate as any definition can be, 

 sanctioned by sixty years or more of usage by 

 the best writers, and expressed in language 

 that is probably as clear and satisfactory as 

 any other that can be invented. It fits easily 

 the energy formula FS = iMV-, and when heat 

 energy and electrical energy are studied, the 

 doctrine of conservation of energy. 



If there is any " existing confusion in the 

 use of the word energy " it is due to modern 

 vsriters who have departed from the good old 

 definition. When they return to it the con- 

 fusion will disappear. 



Wm. Kent 



SCIENTIFIC BOOKS 



The Vegetation of a Desert Mountain Range. 



By Forrest Sheeve. Carnegie Inst. Wash. 



Pub. 217. Washington, 1915. 8vo. 112 pp., 



18 figs., 36 pis., 1 chart. 



This book is addressed especially to workers 

 in physiological plant ecology, but it should be 

 valuable, also, to students of physiographic 

 ecology and to those whose interest lies pri- 

 marily in the floristic aspects of vegetations. 

 Furthermore, all who respond to the undefina- 

 ble call of deserts and mountains will sense the 

 impulse that leads to pack-saddle and sleeping- 

 bag, if they wiU but glance at the wonderfully 

 good half-tone illustrations here brought 

 forth. It is a little to be regretted that these 

 plates, at the back of a rather special scientific 

 monograph, may not reach nearly all who 

 might derive much pleasure and profit from 

 them. This is a characteristic of good ecolog- 

 ical work, that it interests not only the special- 

 ist in out-of-door biology, but also nature-lov- 

 ers in general and non-ecological scientists. 



Perhaps the most striking general feature of 

 the monograph lies in the fact that Shreve's 

 presentation of his very thorough knowledge of 

 this mountain range does not stop vdth pic- 

 tures and descriptions, nor does it depend, 

 for its scientific interest, upon general theories 

 as to how the various features considered may 

 be related. He goes much farther, and de- 

 votes more than half the book to measure- 

 ments of climatological conditions and actual 

 correlations between these and plant distri- 

 bution. Eealizing the fundamental impor- 

 tance of climatic features in determining 

 plant activities, students of plant distribution 

 have long wished for this sort of treatment, 

 but only a few have thus far found the oppor- 

 tunities, the patience and the insight, to cor- 

 relate quantitative climatic measurements 

 with ecological observations. This publication 

 will probably have its greatest value to eco- 

 logical science in the suggestions that it offers 

 as to quantitative methods of attack upon the 

 vegetation-climate correlation. 



The Santa Catalina range lies near Tucson, 

 Arizona, and rises from a basal elevation of 

 about 3,000 feet to a height of 9,150 feet, thus 



