110 THE PRINCIPLES OF SCIENCE. [CHAP. 



The operator will readily collect the various conclusions 

 in the manner described in previous pages, as, for in- 

 stance that A is always C, that not-C is not-B and not- 

 A ; and not-B is not-A but either C or not-C. The results 

 are thus to be read off exactly as in the case of the 

 Logical Slate, or the Logical Abacus. 



Disjunctive propositions are to be treated in an exactly 

 similar manner. Thus, to work the premises 



A = AB -I- AC 

 B .|- C = BD -I- CD, 



it is only necessary to press in succession the keys 

 A (left), copula, A (right), B, -I- , A,C, full stop. 



B (left), -I- , C, copula, B (right), D, ] , C,D, full stop. 

 The combinations then remaining will be as follows 

 ABCD aBCD abcD 



ABcD aBcD abed. 



A&CD a&CD 



On pressing the left-hand key A, all the possible com- 

 binations which do not contain A will disappear, and the 

 description of A may be gathered from what remain, 

 namely that it is always D. The full-stop key restores all 

 combinations consistent with the premises and any other 

 selection may be made, as say not-D, which will be found 

 to be always not-A, not-B, and not-C. 



At the end of every problem, when no further questions 

 need be addressed to the machine, we press the Finis 

 key, which has the effect of bringing into view the whole 

 of the conceivable combinations of the alphabet. This 

 key in fact obliterates the conditions impressed upon the 

 machine by moving back into their ordinary places those 

 combinations which had been rejected as inconsistent with 

 the premises. Before beginning any new problem it is 

 requisite to observe that the whole sixteen combinations 

 are visible. After the Finis key has been used the machine 

 represents a mind endowed with powers of thought, but 

 wholly devoid of knowledge. It would not in that con- 

 dition give any answer but such as would consist in the 

 primary laws of thought themselves. But when any pro- 

 position is worked upon the keys, the machine analyses 

 and digests the meaning of it and becomes charged with 

 the knowledge embodied in that proposition. Accordingly 

 it is able to return as an answer any description of a term 



