2 55 
by signs the action of machinery. 
Each of the vertical lines, representing any part of the ma- 
chine, must now he connected with that representing the 
part from which it receives its movement, by an arrow of 
such a kind as the preceding table indicates ; and if any part 
derives motion from two or more sources, it must be con- 
nected by the proper arrows with each origin of its move- 
ment. It will in some cases contribute to the better under- 
standing of the machine, if those parts which derive move- 
ment from two or more sources have their names connected 
by a bracket, with two or more vertical lines, which may be 
employed to indicate the different motions separately. Thus 
if a shaft has a circular as well as a longitudinal motion, the 
two lines attached to its name should be characterised by a 
distinguishing mark, such as (vert, motion) and (circ. motion). 
Whenever any two or more motions take place at the same 
time, this is essential ; and when they do not, it is convenient 
for the purpose of distinguishing them. 
All machines require, after their parts are finished and put 
together, certain alterations which are called adjustments. 
Some of these are permanent, and, when once fixed by the 
maker, require no further care. Others depend on the nature 
of the work they are intended to perform, as in the instance 
of a corn mill ; the distance between the stones is altered 
according to the fineness of the flour to be ground : these 
may be called usual adjustments ; whilst there are others 
depending on the winding up of a weight, or spring, which 
may be called periodic adjustments. As it is very desirable 
to know all the adjustments of a machine, a space is reserved, 
below that in which the connections of the moving parts are 
exhibited, where these may be indicated ; if there are many 
