692 SCIENCE PROGRESS 



Multiplier"; the telegram, the algebraical X, the metaphor and the Braille 

 alphabet to indicate that "Symbolism" is "the tongue of efficiency, and in some 

 respects also its brain " ; memory as a "groupish and efficiental" organisation ; and 

 the superior efficiency of the Christian method to retaliation. 



An efficient process is defined as " one in which the available results exceed the 

 expenditure." Whatever may be thought of this definition, with its attempt to 

 translate all efficiency into quantitative terms, it is not to be understood as 

 confined to purely economic or material advantage. The reference to " elemental 

 chemical ideas," such as the "carbon molecule," as concepts for dealing "efficiently 

 with phenomena" is in itself enough to remove any such misunderstanding. 

 Mechanical and industrial efficiencies are examined and analysed ; but the mental 

 receives its appreciation as the primary source, and the educational, the social, the 

 ethical, and even the religious efficiencies are discussed. In the appendix on " The 

 Categories and a General Philosophy of Life," the principles of efficiency are 

 traced in the fundamental notions of the mind. 



Re-use is emphasised as a primitive and, " in a sense, fundamental source of 

 efficiency"— memory re-uses perceptions, an idea or process may be applied many 

 times in or out of its original connection. The "Group" combines economy and 

 re-use. A slide rule is a " multiplicative group system." We utilise " Externality" 

 as an efficient principle when we use external things or entities. These principles 

 and many others, such as directive agencies, rhythm, and the significance of limita- 

 tions, are examined, classified, and discussed. 



The chapter on " Dialectic " lays stress on the advantages resulting from unex- 

 pected developments. The depredations of the Colorado Beetle led to improved 

 methods of potato culture ; Perkin accidentally produced mauve when studying 

 quinine. This chapter may confirm the general impression of some readers that, 

 like logic, the general science of efficiency is interesting but sterile. We learn, on 

 this rendering, how some efficiencies have come, but not how to deal with any 

 particular situation. But a study of methods, if adequate, should lead to better 

 understanding and hence to improved practice. 



Exercises are appended to the various chapters to add to the value of the work 

 if used as a textbook. 



Joshua C. Gregory. 



The Birth-Time of the World and other Scientific Essays. By J. Joly, M.A., 

 Sc.D., F.R.S. [Pp. xvi + 307, with 28 plates and 15 illustrations.] 

 (London : T. Fisher Unwin, Ltd. 10s. 6d. net.) 



This volume contains twelve essays, being for the greater part studies which have 

 been contributed to scientific reviews or delivered as popular lectures during 

 recent years. Some are expositions of views the scientific basis of which may be 

 regarded as established ; others are attempts to solve problems which cannot be 

 approached by direct observation. In all of them we find that charm of style and 

 lucidity of expression which is so noted a characteristic of Dr. Joly's writings and 

 lectures. 



The essay which gives its name to the book is a summary of results obtained 

 by various methods concerning the "age of the Earth," *.*., the lapse of time from 

 that epoch at which sediment began to deposit on the underlying floor of igneous 

 and metamorphic rocks and the vapours began to condense from the hot and heavy 

 atmosphere. The various methods of investigation referred to are those connected 

 with the mass of the sediments, with the amount of sodium in the ocean, and with 



