xiv PREFACE TO THE SECOND EDITION. 



logical student to test his skill in the solution of inductive 

 logical problems, I have given (p. 127) a series of ten 

 problems graduated in difficulty. 



To prevent misapprehension, it should be mentioned 

 that, throughout this edition, I have substituted the name 

 Logical Alphabet for Logical Abecedarium, the name applied 

 in the first edition to the exhaustive series of logical 

 combinations represented in terms of A, B, C, D (p. 94). 

 It was objected by some readers that Abecedarium is a 

 long and unfamiliar name. 



To the chapter on Units and Standards of Measure- 

 ment, I have added two sections, one (p. 325) containing 

 a brief statement of the Theory of Dimensions, and the 

 other (p. 319) discussing Professor Clerk Maxwell's very 

 original suggestion of a Natural System of Standards for 

 the measurement of space and time, depending upon the 

 length and rapidity of waves of light. 



In my description of the Logical Machine in the 

 Philosophical Transactions (vol. 160, p. 498), I said 

 " It is rarely indeed that any invention is made without 

 some anticipation being sooner or later discovered ; but up 

 to the present time I am totally unaware of even a single 

 previous attempt to devise or construct a machine which 

 should perform the operations of logical inference ; and it 

 is only, I believe, in the satirical writings of Swift that an 

 allusion to an actual reasoning machine is to be found." 

 Before the paper was printed, however, I was able to refer 

 (p. 518) to the ingenious designs of the late Mr. Alfred 

 Smee as attempts to represent thought mechanically. 

 Mr. Smee's machines indeed were never constructed, and, 

 if constructed, would not have performed actual logical 

 inference. It has now just come to light, however, that 

 the celebrated Lord Stanhope actually did construct a 

 mechanical device, capable of representing syllogistic 

 inferences in a concrete form. It appears that logic was 

 one of the favourite studies of this truly original and 

 ingenious nobleinan. There remain fragments of a logical 



