402 Notices respecting New Books. 



the example of Faraday, viz. the tenacity with which it will cling 

 to a conception as likely to prove true and important in spite of 

 repeated failures to verify it by experiment — which is of course 

 a totally different thing from its being negatived by experiment. 

 Thus Faraday first attempted to demonstrate a relation between 

 magnetism and light in 1822 ; and though he frequently renewed 

 the attempt, he was unsuccessful until, partly by accident, he ob- 

 tained a result in 1845. In this case his tenacity was rewarded 

 with success. Another series of attempts to demonstrate a reci- 

 procal re]ation between gravity and electricity proved unavailing to 

 the end. This instance very appropriately leads up to the remark, 

 that " frequently the exercise of the judgment ought to end in ab- 

 solute reservation," the power to maintain this state being yet an- 

 other characteristic of the philosophic mind. 



In concluding our notice we will venture to do no more than to 

 mention a single thought which has occurred to us several times 

 while reading the work before us. It is this, that although given 

 trains of reasoning, whether deductive or inductive, command 

 universal assent, yet as soon as we get into a discussion of what 

 constitutes the cogency of the reasoning, we are landed in the 

 region of doubt and debate. This might be thought a paradox were 

 it not so well known to be true. No one doubts the conclusiveness 

 of the deductive reasoning by which Euclid proves his forty-seventh 

 proposition ; but let the question be started, "What is deductive 

 reasoning ? and whence does it derive its conclusiveness ? and we 

 shall find the highest authorities giving different answers. A like 

 remark applies to the far more complicated process by which the 

 universal gravitation of matter is proved. Several of Mr. Jevons's 

 logical doctrines might be taken in illustration of these remarks ; we 

 will mention one or two. 



1. Mr. Jevons, supported by high authority, regards the formula 

 " Whatever is, is," as a fundamental law of thought — though 

 Shakspeare, to all appearance, regarded it as mere matter for a 

 joke, and Locke treated its pretensions with scorn, and Mr. Mill 

 thought the treatment just*. 



2. Mr. Jevons tells us (vol. i. p. 48) that " in ordinary lan- 

 guage the verbs is and are express mere inclusion more often than 

 not. ' Men are mortals ' means that men form part of the class 

 mortal." There is, of course, a fundamentally different view of the 

 case, according to which the word is merely predicates of men the 



* It might be supposed that the words " Whatever is, is," mean " What- 

 ever exists, exists ;" but this is, apparently, not the case, its meaning 

 being "X is X ; " e.g. a circle is a circle, or, as Mr. Jevons put it, "a 

 thing at any moment is perfectly identical with itself." So that the clown 

 in Twelfth Night seems to have understood the maxim when he said, 

 " For as the old hermit of Prague, that never saw pen and ink, very 

 wittily said to a niece of King Gorboduc, ' That, that is, is ;' so I being 

 master parson, am master parson." The reference to Locke is Book IV. 

 c. 7> of the ' Essay concerning Human Understanding ;' that to Mr. 

 Mill is p. 408 of f An Examination of Sir William Hamilton's Philosophy.' 



