PERFORMANCE OF LOGICAL INFERENCE. 
511 
into which a rod is thrown by a predicate key. The fourth position lies one half inch 
beyond the third. The four positions evidently correspond to the four classes into 
which combinations were classified in the previous part of the paper as follows : — 
Second Position. — Combinations excluded from the sphere of the premise. 
First Position. — Combinations included, but consistent with the premise. 
Third Position. — Temporary position of combinations contradicted by the premise : 
also temporary position of combinations excluded from some of the alternatives of a 
disjunctive predicate. 
Fourth Position. — Final position of contradictory or inconsistent combinations. 
40. Let us now follow out the motions produced by impressing the simple proposition 
A is B 
upon the machine, all the rods being at first in the initial or first position. The keys 
to be pressed in succession are — 
First. The subject key, A. 
Second. The copula key. 
Third. The predicate key, B. 
Fourth. The full-stop key. 
The subject key A has the effect of throwing all the a rods from the first into the 
second position, the back rods rising and the front rods falling inch. 
The copula key will in this case have no effect, for, as seen in fig. 9 (Plate XXXIV.), 
it acts only on rods in the third position, of which there are at present none. 
The predicate key (fig. 11) does not act upon such of the rods (those marked a) as 
are in the second position, but it acts upon those in the first position, provided they have 
pins opposite the lever. The effect thus far will be that the a rods are in the second posi- 
tion, the A l) rods in the third, while the A B rods remain undisturbed in the first posi- 
tion. An analysis has been effected exactly similar to that explained above (§ 23, p. 505). 
41. The full-stop key being now pressed has a double effect. It acts only on a single 
lever at the front of the machine (figs. 2 & 7), but the front rods all have in the space 
opposite to the lever two pins one inch apart (fig. 1). These pins we may distinguish 
as the a and (3 pins, the a pin being the uppermost. While a rod is in the first posi- 
tion the lever passes between the pins and has no effect ; but if the rod be lowered 
\ inch into the second position, the lever will cause the rod to return to the first posi- 
tion by means of the a pin ; but if the rod be raised into the third position, the /3 pin 
will come into gear, and the rod will be pushed \ inch further into the fourth position. 
Now in the case we are examining, the AB’s are in the first position and will so remain ; 
the As are in the second and will return to the first, the AAs are in the third, and will 
therefore proceed onwards to the fourth. The reader will now see that we have effected 
the classification of the combinations as required into those consistent with the premise 
A is B, whether they be included or not in the term A, and those contradicted by the 
premise which have been ejected into the fourth position. An examination of the 
figures 6-13 will show that only one lever (fig. 8) moved by the Finis key affects rods in 
