514 
PEOFESSOE JEVONS ON THE MECHANICAL 
and the b’ s ; the predicate keys, out of the remaining A B’s, throw the c’s and d’ s into the 
third position ; and the full stop completes the separation of the consistent and contra- 
dictory combinations in the usual manner. 
48. It yet remains for us to consider a proposition with a disjunctive term in subject, 
predicate, or both members. For such propositions the conjunction keys are requisite, 
that adjoining the subject keys (tig. 4) for the subject, and the other for the predicate. 
These keys act in opposition to each other, and each is opposed, again, to its corre- 
sponding letter keys. Thus while the subject keys act on levers at the back of the 
machine (Plate XXXIII. fig. 3), the subject conjunction key acts on the lever r in front, 
while the predicate conjunction key t is at the back. These levers are shown in their full 
size in figs. 10 & 12, and are seen to differ from all the other levers in having the edge v 
moving on small wire hinges n in such a way that it can exert force upwards but not 
downwards. The lever can thus raise the rods ; but in case it should strike a pin in 
returning, the edge yields and passes the pin without moving the rod. In connexion 
with these levers each rod has two pins (figs. 1 & 2) at a distance of only \ an inch, and 
the peculiar effect of these pins will be gathered from figs. 10 & 12 (Plate XXXIV.). 
Thus if we press in succession the predicate keys 
A or B, 
the key A will throw the a’s into the third position. The conjunction key will now act 
upon the a pins of the A’s and move them into the second position, and at the same time 
upon the j3 pins of the a’s and return them into the first position. The key B now 
selects from the a’s those which are b’s, and puts them into the third position ready for 
exclusion by the full stop, which will also join to the a B’s still remaining in the first 
position the A’s which were temporarily put out of the way in the second position. 
Should there be, however, another alternative, as in the term 
A or B or C, 
the conjunction key would be again pressed, which gives the a b’s a new chance by 
returning them to the first, and the key C selects only the a b cs for exclusion. The 
action would be exactly similar with a fourth alternative. 
49. The subject conjunction key is similar but opposite in action. If the subject key 
A be pressed it throws the a’s into the second position; the conjunction key then acts 
upon the « pin of the a’s returning them to the first position, and also upon the /3 pin 
of the A’s, sending them to a temporary seclusion in the third position. The key B 
would now select the a b’s for the second position ; the conjunction key again pressed 
would return them, and add the a B’s to those in the third, and so on. The final result 
would be that those combinations excluded from all the alternatives would be found in 
the second position, while those included in one or more alternatives would be partly in 
the first and partly in the third positions. 
In the progress of a proposition the copula key would now have to be pressed, and 
when the subject is a disjunctive term its action is essential. It has the effect (fig. 9) 
