518 
ON THE MECHANICAL PERFORMANCE OF LOGICAL INFERENCE. 
to search the works of two very different but leading thinkers, Mr. J. S. Mill and Sir 
W. Hamilton, without meeting the name of Dr. Boole, or the slightest hint of his great 
logical discoveries ; and other eminent logicians, such as Professor De Morgan or Arch- 
bishop Thomson, barely refer to his works in a few appreciative sentences. This unfor- 
tunate neglect is partly due to the great novelty of Boole’s views, which prevents them 
from fitting readily into the current logical doctrines. It is partly due also to the obscure, 
difficult, and, in many important points, the mistaken form in which Boole put forth 
his system ; and my object will be fully accomplished should this machine be considered 
to demonstrate the existence and illustrate the nature of a very simple and obvious 
method of Indirect Inference of which Dr. Boole was substantially the discoverer. 
Mathematical System ; but it is significant that he omits the process of mathematical deduction where it is in 
the least complex, and merely quotes Boole’s conclusions. Thus we have the anomalous result that in a treatise 
on Logical Deduction, the reader has to look elsewhere for processes which, according to Boole, must form the 
very basis of Deduction. 
Note to § 7. 
It has been pointed out to me by Mr. White, and has also been noticed in * Nature ’ (March 10th, 1870, 
vol. i. p. 487), that in the year 1851, Mr. Alfred Smee, F.R.S., the Surgeon of the Bank of England, published 
a work called ‘ The Process of Thought adapted to words and language, together with a description of the 
Relational and Differential Machines ’ (Longmans), which alludes to the mechanical performance of thought. 
After perusing this work, which was unknown to me when writing the paper, it cannot be doubted that 
Mr. Smee contemplated the representation by mechanism of certain mental processes. His ideas on this subject 
are characterized by much of the ingenuity which he is well known to have displayed in other branches of 
science. But it will be found on examination that his designs have no connexion with mine. His represent 
the mental states or operations of memory and judgment, whereas my machine performs logical inference. So 
far as I can ascertain from the obscure descriptions and imperfect drawings given by Mr. Smee, his Relational 
Machine is a kind of Mechanical Dictionary, so constructed that if one word he proposed its relations to all other 
words will be mechanically exhibited. The Differential Machine was to he employed for comparing ideas 
and ascertaining their agreement and difference. It might be roughly likened to a patent lock, the opening of 
which proves the agreement of the tumblers and the key. 
It does not appear, again, that the machines were ever constructed, although Mr. Smee made some attempts 
to reduce his designs to practice. Indeed he almost allows that the Relational Machine is a purely visionary 
existence when he mentions that it would, if constructed, occupy an area as large as London. — October 10, 1870. 
