163 Description of a mechanical Instrument to work 



up the row of pence. If I should have 55. 4c?. I set down 

 the 4f?. under the bill, and bring back the red figures 360, 

 &c. again before the index ; then, with the brass handle I 

 move roynd the wheel 3 divisions, and a;o on with the row 

 of shillings, &c. 



This addition-wheel has cost me much time and thought; 

 bi.it should it be honoured with the approbation of the So- 

 ciety, I shall feel myself much gratified. 

 I am, sir, 



Your humble servant, 



No. 4, Wood-Street, Spa-fields, Jan. 21, 1812. J. GOSS. 



To C. Taijlor, M.D. Sec. 



Reference to the Engraving of Mr. J. Goss's Instrument 

 to work the Addition of Numbers in Arithmetic. Plate 

 V. Fig. 1, 2, 3, 4. 



This instrument consists of a brass hoop, fixed to a flat 

 circular plane of wood; this hoop is divided on its upper 

 edge into 180 ratchet or saw-like teeth, and the circle has 

 a riumber of radii lines of figures upon its face, in divisions 

 corresponding with the teeth; also of a supporting circle, 

 having a fixed index reaching across those lines of figures ; 

 and a circular row of 20 divisions, and another of 50, cor- 

 respondent to the ratchet teeth ; and of a brass central 

 index which takes into the teeth, and will turn the ring ia 

 one direction only, to one certain place or stop ; and then, 

 the numbers on the circle, close to the fixed index, will 

 show the sum total of the difierent numbers to which it 

 has been turned round, at any number of intervals. Fig. 1. 

 is a plan, showing a portion of the moveable hoop and 

 circle, and the numbers which are upon its face. Fig. 2. 

 is a section of the instrument, answering to the same. 

 Fitr. 3. is a plan, on a smaller scale, of the instrument 

 on the under side; and fig, 4. an edge view corre- 

 sponding with it ; the same letters of reference are used 

 in all the figures. AA represents the principal upper 

 or moveable circle, on which some of the numbers are 

 marked; this is attached by a centre pin R to another cir- 

 cle BR, figs. 2, 3, and 4, which is held in the hand when 

 the instrument is used; these two circles turn round freely 

 upon each other, and upon the centre of the upper one a 

 rfidial lever, or index, CL, is fixed, which has a free motion 

 round the cent'c pin R. The circle AA has a ring or 

 hoop of brass MM, fixed round its circumference, which 

 is cut into 160 serrated teeth, as show^u in fig. 2. . The 



centre 



