vi.j THE INDIRECT METHOD OF INFERENCE. 107 



The Logical Machine. 



Although the Logical Abacus considerably reduced the 

 labour of using the Indirect Method, it was not free from 

 the possibility of error. I thought moreover that it would 

 afford a conspicuous proof of the generality and power of 

 the method if I could reduce it to a purely mechanical 

 form. Logicians had long been accustomed to speak of 

 Logic as an Organon or Instrument, and even Lord Bacon, 

 while he rejected the old syllogistic logic, had insisted, in 

 the second aphorism of his " New Instrument," that the 

 mind required some kind of systematic aid. In the 

 kindred science of mathematics mechanical assistance of 

 one kind or another had long been employed. Orreries, 

 globes, mechanical clocks, and such like instruments, 

 are really aids to calculation and are of considerable 

 antiquity. The Arithmetical Abacus is still in common 

 use in Russia and China. The calculating machine of 

 Pascal is more than two centuries old, having been con- 

 structed in 1642-45. M. Thomas of Colmar manufactures 

 an arithmetical machine on Pascal's principles which is 

 employed by engineers and others who need frequently 

 to multiply or divide. To Babbage and Scheutz is due 

 the merit of embodying the Calculus of Differences in a 

 machine, which thus became capable of calculating the 

 most complicated tables of figures. It seemed strange 

 that iu the more intricate science of quantity mechanism 

 should be applicable, whereas in the simple science of 

 qualitative reasoning, the syllogism was only called an 

 instrument by a figure of speech. It is true that Swift 

 satirically described the Professors of Laputa as in pos- 

 session of a thinking machine, and in 1851 Mr. Alfred 

 Smee actually proposed the construction of a Eelational 

 machine and a Differential machine, the first of which 

 would be a mechanical dictionary and the second a mode 

 of comparing ideas ; but with these exceptions I have 

 not yet met with so much as a suggestion of a reasoning 

 machine. It may be added that Mr. Smee's designs, though 

 highly ingenious, appear to be impracticable, and in any 

 case they do not attemptthe performance of logical inference. 1 



1 See his work called The Process of Thought adapted to Words and 

 Language, together with a Description of the Relational and Differ- 



