122 PROCEEDINGS. 



was afterwards printed in Mind, Vol. iv., pp. 192 — 210. The 

 materials in my possession did not enable me to give a complete 

 or systematic account of Stanhope's views on logic, nor was that 

 the object of my paper. What I endeavoured to do, was to bring 

 out, so far as I had been able to collect them from scattered and 

 fragmentary hints, those points in his system which serve to 

 illustrate and explain the working of his Demonstrator. 



For a full description of the instrument and the manner of 

 working it, the members are referred to the paper above cited.* 



The Stanhope Arithmometer. 



I am not aware that any account of this instrument has hitherto 

 been published, though its existence has long been known, in fact 

 there are no fewer than four in existence ; one is in the hands of 

 the present Earl, (the great grandson of the inventor), two others 

 of like construction, have come into the possession of General 

 Babbage, who found them among the relics of his celebrated father 

 Charles Babbage, and the fourth, a much smaller and less effective 

 instrument, here exhibited, has become by deed of gift, my own 

 property. It was probably one of the earliest that Stanhope 

 devised and caused to be executed. 



On the face of the instrument are twelve moveable discs of 

 which nine are for pounds, namely units, tens, hundreds, &c, up 

 to hundreds of millions, and the other three are for shillings, 

 pence and farthings, respectively, namely twenty shillings, twelve 

 pence and eight farthings, the last mentioned being constructed 

 for eight instead of four farthings, in order, no doubt, that the 

 spindle carrying the disc might not be inconveniently small. The 

 instrument is nine inches long, three inches wide, and nearly an 

 inch deep. It is of excellent workmanship and bears the inscrip- 

 tion. " Visct. Mahon Inv. 17/80 Jas. Bullock Fecit," 



The following description applies chiefly to the pound or decimal 

 discs, but much of it applies also to the others. The discs lie level 

 with the face or upper plate, in openings made to receive them. 

 Round each disc there is engraved a circle containing the ten 

 digits, 0, 1, 2 ... 9, the alternate discs having these figures arranged 

 in the reverse order. On each disc, near to its circumference, 

 there is a series of equidistant holes, each hole being situated 

 opposite one of the figures in the surrounding circle. A hand or 

 pointer on the disc coincides with the centre and one of the holes. 



The process of addition is performed by inserting the point of 

 a style in the hole opposite the figure in the circle surrounding 

 the disc, and moving the disc in the direction 0, 1, 2, 3, tfec, until 



* Mr. Harley has presented to the Society a separate copy of his paper 

 and also a photograph of the instrument taken by Mr. Hurwood of 

 Liverpool-street, Sydney. 



