168 On the Mechanical Performance of Logical Inference. [Jan. 2(3, 



Metal, element, 

 Metal, not element. 

 Not metal, element. 

 Not metal, not element. 



But according to the second Law of Thought, nothing can combine con- 

 tradictory attributes, and this law prevents us from supposing that iron 

 can be not metal, while the first premise affirms that it is metal. The 

 second premise again prevents our supposing that the combination metal, 

 not element can exist. Hence the only combination of properties which 

 the premises allow us to affirm of iron is metal, element. In a similar 

 manner a complete solution of any logical problem may be effected by 

 forming the complete list of combination, in which the terms of the pro- 

 blem can manifest themselves, and then striking out such of the combi- 

 nations as cannot exist in consistency with the conditions of the problem. 



The logical machine actually constructed represents the combina- 

 tion, 1G in number, of four positive terms, denoted by A, B, C, D, aud 

 their corresponding negatives, a, b, c, d. The instrument is provided 

 with eight keys, representing these terms when appearing in the subject of 

 a proposition, with eight keys, placed to the right hand of the former, 

 representing the terms when occurring in the predicate of a proposition, 

 and with the certain operation keys denoting the copular of the proposi- 

 tion, the full stop at the end of it, and the conjunction or, according as it 

 occurs in the eulycet or tredicate. There is also a key denoting the finis 

 or end of an argument, which has the effect of obliterating any previous 

 impressions, and making the machine a tabula nasa. If, now, each of the 

 letter terms A, B, C, D be taken to represent some logical term or noun, 

 and propositions concerning them be, as it were, played upon the machine, 

 as upon a telegraphic instrument, the machine effects thereby such a 

 classification and selection of certain rods representing the 16 possible 

 combinations of the terms, that only those combinations consistent with 

 the propositions remain indicated by the machine at the end of the opera- 

 tions. When once a series of propositions is thus impressed upon the ma- 

 chine, it is capable of exhibiting an answer to any question which may be 

 put to it concerning the possible combinations which form any class. 



The machine thus embodies almost all the powers of Boole's logical 

 system up to problems involving four distinct terms, and to represent pro- 

 blems of any complexity involving any number of terms only requires the 

 multiplication of the parts of the machine. The construction involves 

 no mechanical difficulties, and depends upon a peculiar arrangement of pins 

 and levers, which it would not be easy to explain without drawings. In 

 this arrangement of the parts the conditions of correct thinking are ob- 

 served ; the representative rods are just as numerous as the laws of 

 thought require, and no rod represents inconsistent attributes. The re- 

 presentative rods are classified, selected, or rejected by the reading of a 

 proposition in a manner exactly answering to that in which a reasoning 



