( 8 7 ) 
the Teeth are not to be cut out into quite (harp 
Points, but blunted a little, as in the Wheel H. 
The Nicety of the whole Machine chiefly confifts 
in placing the Center a and b , or (which amounts to 
the fame thing) after having chofen the Breadth of 
the BrafsBottoms, in determining the Diameter of 
the uppermoft Wheel : For if that fliould prove fo 
large, as that the two Wheels H and G fliould very 
near touch one another, the Tooth of Communica- 
tion will be fhort, its Operation will be of a (mail 
Force, and the Wheels themfelves will require a very 
great Exa&nefs, left by turning about the Wheel H, 
and the Tooth of Communication (landing in the 
Pofition as it is reprefented in Fig . a Tooth of 
the Wheel H may touch it, and flop the Motion, 
Whereas,on the other hand,fuppo(ing the Centers at 
the fame Diftance, and the Diameters of both Wheels 
lefs, the Tooth of Communication will be longer: 
then fuch an Exacftnefs is not requir’d in the Wheel, 
yet more Force is neceflary for making the Tooth 
of Communication lay hold the better. Furthermore, 
it will be well for you to make the undermoft com- 
mon Tooth-Wheel as large as you can. 
From the Conftruction of this firft Syftem, with 
which the 3d, 5th, 7th, &c. entirely agree, one may 
eafily imagine the xd, 4th, 6th, 8th, &c. for every 
thing there alfo is the lame, except only, that it is 
inverted ; fo that what in the firft (lands on the 
Right-hand, is on the Left in the fecond. 
The Plate for Multiplication has on irs hollow 
Axis, as it is faid before, two Shoulders, the lower- 
mod of which is very (mall, the Sum of its Height, 
the Thicknefs of the Plate of the Wheel mm, and of 
^ M the 
