MECHANICS AND USEFUL ARTS. 81 



usual four figures of primitive number ; there are some small specimens of 

 other tables. The figures are, as they ought to be, punchy ; the justification, 

 as the printers call it, is perfect. The differences are not printed ; the print- 

 ing part was not carried far enough for this. 



Calculation by machinery, with results told by the insentient calculator 

 itself, is now an accomplished fact. It does not excite its proper interest, 

 because the unfinished attempt of the original inventor has been for many 

 years before the world. But the time may come when this first actual suc- 

 cess will be quoted as the commencement of a long and singular chain of 

 adaptations. 



JOKES' SUMMATOK. 



This is an instrument designed to perform the addition of numbers. It 

 consists of a circular card, upon which the numerals from one up to one 

 hundred, are printed at the points of intersection of a spiral line with a num- 

 ber of radial lines (on the instruments constructed are one hundred of the 

 latter), the figures increasing in amount as they approach towards the cen- 

 tre of the card. The card is hung by a central pin to and behind a light 

 circular plate of wood, which hides all of it except a portion which is visi- 

 ble through a horizontal slot, extending from the circumference towards the 

 centre. Upon the outer edge of this plate, figures from one to one hun- 

 dred are printed in legible characters, the tens, twenties, thirties, etc., being 

 connected in groups by strong lines, and printed in dark characters to give 

 greater facilities in finding any desired number. Surrounding the plate is a 

 ring of wood, which is attached co the card, and moves with it around the 

 centre-pin; in its periphery are one hundred indentations, corresponding 

 with the number of the radial lines, and with the figures printed around the 

 edge of the plate. A' small index slides in the slot of the plate, its motion 

 being coincident with that of the spiral line on the card over which it always 

 is, approaching to, or receding from the centre, as the card is turned from 

 right to left, or vice versa. 



The operation of adding is performed thus : The index is placed at 

 zero by turning the card backwards by means of a crank handle intended 

 for that purpose; the indentation over the figure equalling the amount of 

 the bottom line of the column to be added is brought by the revolution of 

 the ring and card just opposite the slot in the circular plate, at which point 

 it is arrested by a stop, against which the finger or pencil used to rotate the 

 ring strikes, when the index will have moved towards the centre, and will 

 mark the amount of the first line of the column to be added. The amount 

 of the next line being taken, and the ring turned, the number shown by the 

 indicator will equal the amount of the first and second lines, and so on. To 

 those persons who are not expert in adding, and do not care to become so, 

 this instrument will no doubt be useful. It is mounted on a near stand, and 

 is a much more convenient and rapid way of adding mechanically, than the 

 old way of slipping balls upon wires stretched in a frame, aud which no 

 doubt is familiar to all. 



