March 27, 1914] 



SCIENCE 



465 



I should be glad if any worker who is able 

 to send photographs will communicate with 

 me as soon as possible so that I might arrange 

 for the receiving and entry of the exhibit. 



C. E. K. Mees 

 Research Laboratory, 

 Kodak Park, 

 Rochester, N. T. 



SCIENTIFIC BOOKS 



Definitions in Physics. By Karl Eugen 

 GcTHE, Ph.D., Professor of Physics in the 

 University of Michigan and Dean of the 

 Graduate Department. New York, The 

 Macmillan Company. 1913. Pp. vii + 

 107. 



A man's convictions are vastly more im- 

 portant than the logical processes by which he 

 reaches them; and his convictions are repre- 

 sented in a large degree by the definitions 

 which he adopts. It follows, therefore, that 

 the appearance of a volume of definitions by a 

 scholar of high standing in any particular 

 field of thought is a matter of some moment. 

 There is danger of taking physics too seri- 

 ously; and nothing is easier than to employ 

 definitions in such a way as to produce in the 

 student-mind what Professor Eranklin calls 

 " a stress of dryness." But when the technical 

 terms of his own science have been collected 

 by a well-known specialist they become a mat- 

 ter of keen interest, and all the more so when 

 that specialist is an experienced and success- 

 ful teacher as is Professor Guthe. 



Definitions grow as our ideas grow. They 

 are not the fixtures of the Medes and Per- 

 sians. Compare the modern definition of the 

 crab with the classical one given in the French 

 Academy's dictionary. Or consider how the 

 resistance term in Ohm's law developed into 

 impedance upon the introduction of alternating 

 currents. Previous to the renaissance forces 

 were defined only in a statical way; anything 

 that would flatten out the muscles of the hand, 

 bend a beam, disturb the configuration of a 

 steelyard, or bring out any other strain re- 

 quiring work was classified as a force; and 

 conversely the term force was used at that 



time to include many ideas, such as speed, 

 impulse, energy and power, which now lie 

 quite without its limits. Shortly after the 

 renaissance the concept of force was enlarged 

 so as to take in the time-rate of change of 

 momentum; later the generalized forces of 

 Lagrange are included. Again the Peltier ef- 

 fect is defined quite difi^erently from what it 

 was before the Thomson effect was discovered. 



A list of definitions is therefore a list of 

 variable quantities and can hardly be regarded 

 as more than a cross-section of the conven- 

 tions agreed upon by the generation which 

 uses them. 



The book under review is one which can not 

 fail to be of the utmost help to any student of 

 general physics. The definitions are arranged 

 under the classical five chapters of physics. 

 Each quantitative concept is, as a rule, first 

 defined in simple English and in terms al- 

 ready explained or assumed; next follows a 

 mathematical expression which may be consid- 

 ered as a repetition of the first definition, and 

 frequently, as an expression of natural law. 

 The definitions are remarkable for their clear- 

 ness, simplicity and brevity; if at any point 

 indefiniteness suggests itself one feels that ad- 

 ditional details have been omitted only to se- 

 cure brevity. This feature is illustrated by 

 the first paragraph in the book which defines 

 physics in a manner which is elegant but so 

 general as to leave doubt in the reader's mind 

 as to whether physics and physical science are 

 one and the same. 



At the outset the author enunciates his 

 conviction that " certain concepts used in 

 physics are deductions and generalizations 

 from individual experience and can not be 

 strictly defined. Such are the concepts of 

 extension (space, with its subdivisions of vol- 

 ume, area, length and direction), time, force, 

 warmth, cold, etc." On the same page, a phys- 

 ical quantity is defined as " a definite concept 

 capable of measurement." 



Every one who thus finds force listed among 

 the indefinables will surely understand that 

 Professor Guthe here means to imply nothing 

 more than that no complete and satisfactory 

 definition has yet been given. For only a few 



