254 
Mr. Babbage on a method of expressing 
motion is communicated ; and it becomes a matter of some 
importance to consider whether, without interfering with the 
sign just selected, some modification might not be intro- 
duced into its minor parts, which, leaving it unaltered in the 
general form, should yet indicate the peculiar nature of the 
means by which the movement is accomplished. 
On enumerating those modes in which motion is usually 
communicated, it appeared that they may be reduced to the 
following. 
One piece may receive its " 
motion from another by being 
permanently attached to it as a 
pin on a wheel, or a wheel and 
pinion on the same axis. 
One piece may be driven by" 
another in such a manner that 
when the driver moves, the other 
also always moves ; as happens 
when a wheel is driven by a 
pinion. 
This may be indicated by an 
arrow with a bar at the end. 
H > 
An arrow without any bar. 
> 
One thing may be attached to 
another by stiff friction. 
An arrow formed of a line in- 
» terrupted by dots. 
I — •— i — •— 
One piece may be driven by 
another, and yet not always move 
when the latter moves ; as is the 
case when a stud lifts a bolt once 
in the course of its revolution. 
By an arrow, the first half of 
which is a full line, and the 
second half a dotted one. 
— *> 
One wheel may be connected 
with another by a ratchet, as the 
great wheel of a clock is attached f 
to the fusee. 
By a dotted arrow with a ratchet 
tooth at its end. 
. ts 
•> 
