165 
at once see, for instance, that the class a, or “dissimilar 
figures, consist of all triangles (B) which have not their 
corresponding angles equal (c) and sides proportional ( d ), 
and of all figures not being triangles (5) which have either 
their angles equal (C) and sides not proportional ( d ), or their 
corresponding sides proportional (D) and angles not equal, 
or neither their corresponding angles equal nor corresponding 
sides proportional.” (Boole, p. 126.) 
The selections as made upon the abacus are of course 
subject to mistake, but only one easy step is required to a 
logical machine, in which the selections shall be made 
mechanically and faultlessly by the mere reading down of 
the premises upon a set of keys, or handles, representing the 
several positive and negative terms, the copula, conjunctions, 
and stops of a proposition. 
Mr. Jevons stated his opinion distinctly that these contri- 
vances possessed a theoretical rather than a practical 
importance. Like the analogous Calculating Machine of 
Babbage or Scheutz, the logical machine would hardly find 
practical employment for the present at least. But its value 
consisted in showing the true nature of logic as a system of 
analysis of the possible combinations of things, in short as 
the highest and simplest form of the doctrine of combinations. 
Not only would the deductive, and especially the inductive 
processes of logic be thus presented in a new and clearer light, 
but the relation of logic, the qualitative doctrine of combina- 
tions, to mathematics the quantitative doctrine of combinations, 
would be defined, and the abstract sciences thus brought into 
harmony and due subordination. 
In the description of his balance given in the last No. of 
the Proceedings, Dr. Joule omitted to mention a fixed 
support against which the scale rests when the counterbalance 
is removed. By this means the wires are kept constantly in 
the same state of tension, and are thus preserved from the 
derangement which might otherwise ensue. 
