June 16, 1916] 



SCIENCE 



853 



that they follow these rules as such rules are 

 usually followed, that is only so far as they 

 conflict with no personal opinion? 



In the above-mentioned note Mr. Hebard ex- 

 presses regret that well-known names should be 

 changed on debatable grounds. In view of this 

 statement it is interesting to note his use in 

 the same paper, page 19, of the name Schisio- 

 cerca serials Thunberg instead of Schisto- 

 cerca americana Drury, a name in common 

 use long before Pedeticum was erected. 

 That the original inclusion of the species 

 americana in the genus LUellula, which makes 

 it a primary homonyra of LUellula americana 

 Linn., a true dragon fly, was a lapsus seems 

 clear for several reasons, a matter too compli- 

 cated for discussion at this time. However, 

 even if granted as obviously a lapsus calami, 

 there appears to be no definite authority in 

 any code of rules for the setting aside of this 

 reference. Thus Mr. Hebard's suppression of 

 the name americana is accepted, but, until a 

 decision is rendered on the ease by the Inter- 

 national Commission, the grounds upon which 

 he suppresses it are certainly debatable, more 

 so, in fact, than those upon which the present 

 writer resurrects the genus Pedeticum. Indeed 

 this action of Mr. Hebard would probably not 

 be sustained by the International Commission 

 if it acts on the case, as its decision would 

 very likely agree with the private opinion of 

 its secretary. Dr. C. W. Stiles, as stated in the 

 authorized quotation here given from a letter 

 written on April 10, 1916 : 



... In the case of Lihellula americanus Drury, 

 1770 (in index of later date) it seems clear that 

 this is a Lapsus calami. 



Without attempting to commit the Commission 

 to any view, I personally would not reject — espe- 

 cially at the present moment — a well-known name 

 like Gryllus americanus sen ScMstocerca americana 

 because of an obvious lapsus calami. 



Dr. L. Stejneger, also a member of the Com- 

 mission on Zoological Nomenclature, author- 

 izes the statement that his present views on 

 this matter coincide with those expressed in the 

 above quotation. 



A. N". Oaudell 

 Bdeeau op Entomology, 

 "Washington, D. C. 



THE CURRENT "DEFINITIONS" OF ENERGY 



To THE Editor of Science: In a communi- 

 cation which appeared in a recent number of 

 Science^ Professor M. M. Garver criticizes the 

 current definitions of energy, such as "the 

 capacity for doing work," the " ability to do 

 work," and the " power of doing work," on the 

 ground that these definitions are not consistent 

 with the concept of energy. The terms " capac- 

 ity " and " ability " do not mean entities, while 

 energy is not only a physical entity but it has 

 the property of conservation. 



It seems to me that Professor Garver's criti- 

 cism is well taken, but the alternative he pro- 

 poses is open to criticism also. For Professor 

 Garver .would have no definition of energy at 

 all or, if it is insisted upon, he would have it 

 based on the principle of the conservation of 

 energy. 



Energy is first introduced in text-books of 

 physics as a mechanical concept. Therefore 

 any definition of energy should form an inte- 

 gral part of a logically developed system of 

 mechanics. It should be the direct and nat- 

 ural result of the dynamical concepts which 

 precede it and should form an adequate basis 

 for the new ideas which follow it. Further it 

 should have such a form as to lend itself easily 

 to a mathematical expression of the definition. 

 Elementary mechanics is usually based upon 

 postulates, such as Newton's laws of motion or 

 the action principle, which involve the con- 

 cept of force. Therefore the definitions of 

 energy and momentum as well as the prin- 

 ciples of the conservation of energy and of 

 momentum should be made the direct conse- 

 quence of the postulates which have been 

 selected as the starting point of the develop- 

 ment of mechanics. This necessitates the defi- 

 nition of energy as the "result of the action 

 of force in space" and the definition of 

 momentum as the " result of the action of 

 force in time." In other words, energy should 

 be defined in terms of work and momentum in 

 terms of impulse. The definition of energy 

 contained in the following extract fulfills these 

 conditions. It is not only consistent, but has 

 the advantage of leading to the mathematical 

 expressions for kinetic and potential energy. 

 1 Science, April 21, 1916. 



