LITERARY NOTICES. 



117 



contrasted with deduction, but that induc- 

 tion is simply an inverse employment of de- 

 duction. Within the last century a reaction 

 has been setting in against the purely em- 

 pirical procedure of Francis Bacon, and 

 physicists have learned to advocate the use 

 of hypotheses. I take the extreme view of 

 holding that Francis Bacon, although he 

 correctly insisted upon constant reference 

 to experience, had no correct notions as to 

 the logical method by which, from particu- 

 lar facts, we educe laws of Nature. I en- 

 deavor to show that hypothetical anticipa- 

 tion of Xature is an essential part of induc- 

 tive inquiry, and that it is the Xewtoniau 

 method of deductive reasoning, combined 

 with elaborate experimental verification, 

 which has led to all the great triumphs of 

 scientific research. 



" In attempting to give an explanation 

 of this view of scientific method, I have first 

 to show that the sciences of number and 

 quantity repose upon and spring from the 

 simpler and more general science of logic. 

 The theory of probability, which enables 

 us to estimate and calculate quantities of 

 knowledge, is then described, and especial 

 attention is drawn to the inverse method of 

 probabilities, which involves, as I conceive, 

 the true principle of inductive procedure. 

 No inductive conclusions are more than 

 probable, and I adopt the opinion that the 

 theory of probability is an essential part of 

 logical method, so that the logical value of 

 every inductive result must be determined 

 consciously or unconsciously, according to 

 the principles of the inverse method of 

 probability. 



"The phenomena of Nature are com- 

 monly manifested in quantities of time, 

 space, force, energy, etc. ; and the observa- 

 tion, measurement, and analysis of the va- 

 rious quantitative conditions or results in- 

 volved, even in a simple experiment, demand 

 much employment of systematic procedure. 

 I devote a book, therefore, to a simple and 

 general description of the devices by which 

 exact measurement is effected, errors elimi- 

 nated, a probable mean result obtained, 

 and the probable error of that mean ascer- 

 tained. I then proceed to the principal, 

 and probably the most interesting, subject 

 of the book, illustrating successively the 

 conditions and precautions requisite for ac- 



curate observation, for successful experi- 

 ment, and for the sure detection of the 

 quantitative laws of Nature. As it is im- 

 possible to comprehend aright the value of 

 quantitative laws without constantly bear- 

 ing in mind the degree of quantitative ap- 

 proximation to the truth probably attained, 

 I have devoted a special chapter to the 

 theory of approximation, and, however im- 

 perfectly I may have treated this subject, I 

 must look upon it as a very essential part 

 of a work on scientific method. 



"It then remains to illustrate the sound 

 use of hypothesis, to distinguish between 

 the portions of knowledge which we owe to 

 empirical observation, to accidental discov- 

 ery, or to scientific prediction. Interesting 

 questions arise concerning the accordance 

 of quantitative theories and experiments, 

 and I point out how the successive verifica- 

 tion of an hypothesis by distinct methods 

 of experiment yields conclusions approxi- 

 mating to but never attaining certainty. 

 Additional illustrations of the general pro- 

 cedure of inductive investigations are given 

 in a chapter on the ' Character of the Ex- 

 perimentalist,' in which I endeavor to show, 

 moreover, that the inverse use of deduction 

 was really the logical method of such great 

 masters of experimental inquiry as Newton, 

 Huyghens, and Faraday. 



" The application of scientific method 

 cannot be restricted to the sphere of lifeless 

 objects. AVe must sooner or later have 

 strict sciences of those Mental and Social 

 phenomena which, if comparison be possi- 

 ble, are of more interest to us than purely 

 material phenomena. But it is the proper 

 course of reasoning to proceed from the 

 known to the unknown — from the evident 

 to the obscure — from the material and pal- 

 pable to the subtile and refined. The phys- 

 ical sciences may therefore be properly 

 made the practice-ground of the reasoning 

 powers, because they furnish us with a great 

 body of precise and successful investiga- 

 tions." 



It is thus evident that the plan of Prof. 

 Jevons's work involves a thorough handling 

 of the most recent questions that have been 

 raised in science and philosophy, and an ex- 

 amination of it will show that he has car- 

 ried out his project in an able and indepen- 

 dent manner. We publish a portion of his 



