OF ARTS AND SCIENCES. 303 



XVIII. 



A NEW LOGICAL MACHINE. 

 By Allan Marquand, Ph. D. 



Presented by Invitation, November 11, 1885. 



During the year 1881 I constructed a logical machine somewhat 

 similar to the well-known machine of Prof. Jevons, and printed logi- 

 cal diagrams for problems involving as many as ten terms.* This 

 earlier instrument and the logical diagrams formed the basis of the 

 machine illustrated on the accompanying plate. The new machine was 

 constructed in Princeton during the winter of 1881-82, by my friend 

 Prof. C. G. Rockwood, Jr., whose mechanical skill and untiring pa- 

 tience gave me invaluable assistance. The machine was made from 

 the wood of a red-cedar post, which once formed part of the enclosure 

 of Princeton's oldest homestead. It measures 32 cm. high by 21 cm. 

 wide and 15 cm. deep. Like the instrument of Prof. Jevons, and 

 that of Prof. Venn, it is constructed for problems involving only 

 four terms, but more readily than either of those instruments admits 

 of being extended for problems involving a larger number of terms. 



The face of the machine (Fig. I.) presents to view sixteen small 

 pointers representing the sixteen logical combinations of the symbols 

 A, B, C, and D, with their negatives a, b, c, d. These combinations 

 are so arranged that all the A combinations are found in the two verti- 

 cal columns to our left, the a combinations in the two vertical columns 

 to the right. The A combinations are subdivided vertically into the 

 B and h combinations, and the a series in like manner. Both are also 

 subdivided horizontally into the C and c combinations, and each of 

 these again into the D and d combinations. Thus the uppermost 

 pointer to the left represents the combination A B C D, the horizon- 

 tally adjoining one A b C D, the next a B C D, and so on until we 

 reach the lowermost to the right, which is a b c d. Below the point- 

 ers may be seen the two operation keys marked 1 and 0, and the four 

 positive and four negative letter keys under their respective symbols. 



* riiilos. Mag., October, 1881, pp. 266-270. 



