PERFORMANCE OF LOGICAL INFERENCE. 
509 
or a conjunction, copula or stop intervenes, the pressure of a corresponding lever or key 
shall execute systematically the required movements of the combinations. 
31. The principles upon which the logical machine is based will now be apparent to 
the reader ; and as the construction of the machine involves no mechanical difficulties of 
any importance, it only remains for me to give as clear a description of its component 
parts and movements as their somewhat perplexing character admits of. 
32. The Machine, which has been actually finished, is adapted to the solution of any 
problems not involving more than four distinct positive terms, indicated by A, B, C, D, 
with, of course, their corresponding negatives, a , b, c, d. The requisite combinations of 
the abecedarium are, therefore, sixteen in number (§ 20, p. 504), and each combination 
is represented by a pair of square rods of bay wood (Plate XXXII. fig. 1), united by a short 
piece of cord and slung over two round horizontal bars of wood ( d , d, figs. 2 & 3), so as to 
balance each other and to slide freely and perpendicularly in wooden collars ( b , b , figs. 2, 3, 
& 4) closed by plain wooden bars (c, c ). To each rod is attached a thin piece of baywood, 
8^ inches long and 1 inch wide (a, a , figs. 2 & 3), bearing the letters of the combination 
represented. Each letter occupies a space of ^ inch in height, but is separated from the 
adjoining letter by a blank space of white paper \\ inch long. Both at the front and 
back of the machine are pierced four horizontal slits, 14 inch apart, extending the whole 
width of the case, and ij? inch in height, so placed that when the rods are in their normal 
position each letter shall be visible through a slit. The machine thus exhibits on its 
two sides, when the rods are in a certain position, the combinations of the abecedarium 
as shown in fig. 5 ; but should any of the rods be moved upwards or downwards through a 
certain limited distance the letters will become invisible as at ff (Plate XXXIII. fig. 5). 
33. Externally the machine consists of a framework, seen in perpendicular section in 
fig. 3 (g, g), and in horizontal section in fig. 4 (g, g), which serves at once to support and 
contain the moving parts. It is closed at the front and back by large doors (h, h, fig. 3), 
in the middle panels of which are pierced the slits rendering the letters of the abecedarium 
visible. 
34. The rods are moved upwards, and the opposite rods of each pair are thus caused 
to fall downwards, by a series of long flat levers seen in section at l, l, l (figs. 2, 3, 6 ... 13). 
These levers revolve on pivots inserted in the thicker part, and move in sockets attached 
to the inner side of the framework. Brass arms ( m , m, figs. 3 & 13), connected by copper 
wires ( n , n ) with the keys of the machine ( 0 , 0 ), actuate the levers, which are caused to 
return, when the key is released, by spiral brass springs (s, s). 
35. The levers communicate motion to the rods by means of brass pins fixed in the 
inner side of the rods (fig. 2). As it is upon the peculiar arrangement of these pins 
that the whole action of the machine depends, the position of each of the 272 pins is 
shown by a dot in fig. 1, in which are also indicated the function of each pin and the 
combination represented by each pair of rods. It is seen that certain pins are placed 
uniformly in all the adjoining rods, as in the rows opposite the words Finis , Conjunction , 
Copula , Full Stop. These may be called operation pins, and must be distinguished from 
