( 16 ) 
muft be placed exa&ly on the Point of a Tooth of 
the Wheel, and by its Revolution catches and turns 
every time but one Tooth of the uppermoft Wheel 
of the preceding Syftem, Aiding over the following 
one (if there be any) without touching it. For this 
reafon the Planes of the Brafs Bottoms in all the 
Syftems ought to incline a little. This will belt ap- 
pear from the Vertical Sedtion, Fig.x . (cut in Fig . i. 
in the Dire&ion from h to/) in which a is the 
Brafs-Bottom, HH the Wood-Bottom, g the Ope- 
rator, i the Groove, f the third common Tooth- 
Wheel, b the fecond Wheel, a the firft or upper- 
moft Ratchet-Wheel, e the Bridge, © the Covering- 
Plate, and $ the Tooth of Communication. I have 
reprefented all thele Pieces of one Thicknefs ; but 
every Artift will eafily know where to add or 
take off 
Fig. 5. ftiews the Plan and true Difpofition of the 
Teeth in the feveral uppermoft Wheels ; that is to 
fay, The Parallel Lines AB and CD ought always 
to cut the Brafs Bottoms (which are like one ano- 
ther in Length and Breadth) length-wife into two 
equal Parts : Then the perpendicular Interfedlion 
E F will determine the Centers a and b , of the two 
Wheels H and G. The Stop r ought every time 
to hold its Wheel in fuch a manner, that the Points 
of two Teeth coincide with the Line AB or CD. 
The Obliquity of the Teeth is the fame in both, 
with this difference however, that in G, which is a 
Wheel of the Syftem A A, (Fig. i.) they are cut 
in from the left to the right, but in H (a Wheel of 
the Syftem BB) from right to the left. I need not 
take notice, that for making the Work more durable, 
