2 53 
by signs the action of machinery . 
do not consist of teeth ; of course every vertical line will not 
have a number attached to it. 
The three lines immediately succeeding this, are devoted 
to the indication of the velocities of the several parts of the 
machine. The first must have, on the indicating line of all 
those parts which have a rectilinear motion, numbers ex- 
pressing the velocity with which those parts move, and if 
this velocity is variable, two numbers should be written, one 
expressing the greatest, the other the least velocity of the 
part. The second line must have numbers expressing the 
angular velocity of all those parts which revolve ; the time 
of revoluion of some one of them being taken as the unit of 
the measure of angular velocity. 
It sometimes happens that two wheels have the same 
angular velocity when they move ; but from the structure of 
the machine, one of them rests one half of the time during 
which the other is in action. In this case, although their 
angular velocities are equal, their comparative velocities are 
as 1 to 2 ; for the second wheel makes two revolutions, whilst 
the other only makes one. A line is devoted to the numbers 
which thus arise, and it is entitled. Comparative Angular 
Velocity. 
The next object to be considered is the course through 
which the moving power is transmitted, and the particular 
modes by which each part derives its movement from that 
immediately preceding it in the order of action. The sign 
which I have chosen to indicate this transmission of motion 
(an arrow), is one very generally employed to denote the 
direction of motion in mechanical drawings ; it will therefore 
readily suggest the direction in which the movement is 
transmitted. There are however various ways by which 
MDCCCXXVI. L 1 
