820 



SCIENCE 



[N. S. Vol. XLIII. No. 1119 



seen on the side, with the ends of the same 

 stylolitic columns forming the etched surfaces. 

 A plane of stylolites may be continuous with 

 one of the pitted surfaces. The sides of the 

 depressions sometimes show the characteristic 

 striations of the stylolitic columns. 



So many examples show the absolute rela- 

 tionship and interdependence of the so-called 

 etched surfaces and the stylolites that there 

 can be no doubt that the two features are one 

 and the same thing. Some solvent action has 

 been exerted upon the surfaces because the 

 areas between the depressions are well rounded 

 in many specimens, but the major depressions 

 are the result of the stylolites. Many speci- 

 mens were found which still retained the usual 

 coating of ferruginous clay. 



W. A. Tarr 



"University of Missouri 



the definition of energy 

 To THE Editor of Science : -Language is an 

 arrangement of words used to express and to 

 convey ideas — and sometimes to conceal- ideas 

 or lack of ideas. More than twenty-one years 

 ago, when compiling my " Mechanical Engi- 

 neers' Pocket-book," I wanted some language 

 in which to convey to students an engineer's 

 idea of energy, and with Rankine, Weisbach 

 and other books at my side, I finally wi-ote the 

 following : 



Energy, or stored work, is the capacity for per- 

 formmg work. It is measured by the same unit as 

 work, that is, in foot-pounds. It may be either 

 potential, as in the case of water stored in a 

 reservoir, capable of doing work by means of a 

 water-wheel, or actual, sometimes called kinetic, 

 which is the energy of a moving body. 



In the several revisions my book has under- 

 gone since 1895 I have never found any rea- 

 son to change the wording of this definition. 

 Wow I find in Professor Garver's article in 

 Science of April 21, 1916, that this definition 

 " conflicts with facts," leads to " logical absurd- 

 ities," is "defective and misleading." 



Desiring to find, for the nest revision of my 

 book, the best possible language, or form of 

 words, in which to convey the idea commonly 

 expressed by the word " energy," that is to get 



the best definition of the word, I have read 

 Professor Garver's article with great care, 

 and I find the following : 



We are acquainted with matter only as that 

 which may have energy communicated to it from 

 other matter, and which may in its turn convey 

 energy to other matter. 



Energy we know only as that which in all nat- 

 ural phenomena is continually passing from one 

 portion of matter to another. 



This latter, and later, conception of energy 

 seeins, to my mind, a long step in advance over the 

 conception of energy as the "capacity of doing 

 work. ' ' 



From these statements we may derive the 

 following definitions : 



Matter. — That which may convey energy to 

 other matter. 



Energy. — That which is continually passing 

 from one portion of matter to another. 



Matter. — That which may convey that which 

 to other that which. 



Professor Garver also says : 



There is no more necessity for a "definition" 

 of energy than there is for a definition of "mat- 

 ter. ' ' Both are known only by their characteristic 

 phenomena; and these characteristics must serve 

 to identify them and to differentiate them from 

 each other. 



But there is a necessity for definitions of 

 both of these terms. The users of my book de- 

 mand them. Every young student demands 

 that a technical term in a text-book be defined 

 in words that are less technical or more ele- 

 mentary than the term itself. For example, I 

 define matter as follows : 



Matter. — Any substance or material that can be 

 weighed or measured. It exists in three forms: 

 solid, liquid and gaseous. A definite portion of 

 matter is called a body. 



The language used to convey ideas of phys- 

 ical phenomena to students of elementary 

 physics should begin with the simplest and 

 most easily understood words. For example, 

 stone, water, air, solid, liquid, gaseous. The 

 stone, water, air have some qualities in com- 

 mon. They occupy space, can be measured or 

 weighed, and can not be put in motion except 



