( pi ) 
Ihorter broader ones, one under the Window of 
Multiplication, the other above the Silver Plate. 
All this together compofes a Machine, by the help 
of which you may perform all the four Arithmetical 
Rules or Operations. The Way of working it, is 
as follows : 
I. As to Addition : For inftance, if you are to 
add 32 and 59 ; becaufe the hindmoft Syftem A A 
in the Figure, which ought to reprefent the Place of 
Unites, is not cover’d, let us take the Syftem BB 
for the Place of the Unites, and the Syftem CCfor 
the Place of the Tens ; turn the Silver-Plates x x 
in theft two Syftems, that the Indexes ww point 
to the two Numbers 5 and 9 ; then make the De- 
terminators //, //, point alfo to 3 and 2 : next take 
one of the two Operators, ex. gr. in B B, and pull it 
down as far as you can, and move it upwards again. 
This done, the Number 1 of the Silver-Plate in BB 
will come by this means under the Index w 7 and 
the Number 6 of the Silver-Plate in the Syftem C C 
under its Index at the fame time, which is 6r, the 
Sum, 5 9 and 2. After this move the Operator of 
the Syftem C C alfo up and down, when inftead of 
6, 9 will come under the Index ; confequently you 
have 91 under the Indexes ww 7 which is the Sum 
requir’d of 5 9 and 32 added together. TheReafon 
of it is plain ; for by pulling down the Operator 
of the Syftem B B fo far, the Stop c of the lower- 
moft or common Tooth- Wheel/ {vid. Syft. A A) 
will Aide over two Teeth of the Ratchet-middle- 
moft Wheel b ; and by moving the Operator up 
again, the fame Stop c will turn the two Ratchet- 
Wheels a and b together, and caufe the Stop r of 
