400 Notices respecting New Books. 



and BD' = *-a= 2a 



/ju n —l 



Any convenient value such as 2 or J may be given to p, ; or if a 

 special number of lines be required, a value may be found to suit. 

 Thus let L be the greatest value that is to be given to /, and m 

 the number of lines required on each side of 0. We shall have 



a + ~L , 1 , a + ~L 



T =fju m , or log fi= - log Y , 



a — L ^ ° m ° a— L 



which determines the value of p,. 



The successive values of B D' are then 



2a 2a 2a 2a 



p-1' p?-V fi 8 -l' V m -l" 



The successive values of B C are simply alternate values of 

 these, namely 



2a 2a 2a 



Plate IX. shows the equipotential lines drawn for a value of 



p-f 



[To be continued.] 



XLV. Notices respecting New Books. 



The Principles of Science : a Treatise on Logic and Scientific Method. 

 By W. St^ley Jevons, M.A., F.B.S., Fellow of University 

 College, London ; Professor of Logic and Political Economy in the 

 Oivens College, Manchester. London : Macmillan and Co. 

 1874 (two vols. 8vo, pp. 463 and 480). 



'"PHIS is in many respects a remarkable book, and particularly 

 - 1 so in. regard to the extraordinary number, variety, and (as far 

 as we can venture to judge) accuracy of the facts which are brought 

 in illustration of the principles and questions discussed. There is 

 indeed scarcely a branch of science which the author has not laid 

 under contribution for purposes of illustration. The work is 

 divided into five books, viz. : — On Formal Logic, Deductive and 

 Inductive ; on Number, Variety, and Probability ; on Methods of 

 Measurement ; on Inductive Investigation ; and on Generalization, 

 Analogy, and Classification. 



We have found it very difficult to state in few words the up- 

 shot of the discussions in these books severally without doing 

 great injustice to their contents. For instance, the first book 

 might be said to be an exposition of formal logic designed to set 

 forth the author's peculiar method of expressing propositions and 

 arguments by symbols, and to lead up to an account of his logical 

 machine — a machine worked by twenty-one keys like a pianoforte, 



