804 PROCEEDINGS OP THE AMERICAN ACADEMY 



The 1 key may be called the restoration key. It prepares the ma- 

 chine for a new problem, by raising all the pointers to the horizontal 

 position. The key may be called the destruction key, as when 

 pressed down it allows the pointers to fall. The function of a letter 

 key is to sustain in the horizontal position the pointers representing the 

 corresponding negative combinations. Thus, if the A key is pressed, 

 the a pointers are sustained; if the b key is pressed, the B pointers are 

 sustained ; and similarly for all the remaining letter keys. 



Turning now to Fig. II., the mechanism by which this is effected will 

 be easily seen. On the inner face of the machine, and corresponding 

 to the pointers, are sixteen drops, some of which are pictured in the 

 horizontal position, and some as fallen. The two operation keys move 

 rectangular frameworks, each consisting of four vertical brass rods 

 fastened together, and carrying pins which reach all of the sixteen 

 drops. The framework of the key moves on the inner, that of the 

 1 key on the outer side of the drops, both horizontally. If we wish 

 to bring all the pointers to the horizontal position and hold them 

 there, both operation keys are pressed down. The 1 key raises all the 

 drops. Releasing first the key, its framework is drawn back by a 

 fixed spring, and by means of its pins holds the drops in position ; on 

 releasing the 1 key, its framework is drawn back so as not to interfere 

 with subsequent operations. Each letter key operates two vertical or 

 two horizontal I'ods, free to revolve on their axes. In each rod are 

 set four pins, conveniently bent, so that when the rods are partially 

 revolved, by pressure of the letter keys, the pins are made to sustain 

 the drops m the horizontal position without raising those which have 

 fallen. The rods return to their original position, by means of small 

 spiral springs, as soon as the pressure of the letter keys is released. 

 The desired motion is communicated to the rods by means of cat-gut 

 strings, there being two such strings from each letter key. Thus the 

 A key operates the two vertical rods which are to hold the a drops ; 

 the h key the rods for holding the B drops ; and the other letter keys 

 in like manner. By this device it will be seen that, if we should press 

 the A key (this holds the a combinations), and then the key, only 

 the A pointers will fall ; or, if both the A and B keys are depressed 

 (this holds the a and h combinations), and then the key, only the 

 A B pointers will fall ; and similarly for the other combinations. 



To utilize the instrument for the solution of logical problems, we 

 first raise all the pointers to tlvs horizontal position. This will indi- 

 cate the state of a logical universe of four terms before the introduc- 

 tion of premises. Now, since the establishment of any combination 



