114 Mr. Howarp GRUBB, 
more conversant with the principle and practical working of the 
system. They may, however, be classified into three heads :-— 
(a). The designing of the machine. 
(b). The working out of the details of construction. 
(c). The putting together of the machine. 
(a). Let us first consider the designing of the machine. What- 
ever difficulties there are in understanding the working of 
a complicated machine from accurate drawings made after the ma- 
chine is completed, or even from the machine itself, much greater 
are the difticulties to be encountered in designing the machine, for 
in this case the designer has neither machine nor drawings to 
guide him, and the only representation of the machine lies in his 
own brain; while, therefore, he mentally plans one part, he has to 
keep in his mind (if he can) the relative positions and actions of 
all the other parts, and frequently to go back in his work and 
modify and remodify various parts in his mind’s eye, and all 
this must be thought out before he puts pen to paper; for after 
all, mechanical drawings represent, not the actions and motions 
of the machine but the appliances (levers, wheels, cams, éc.), by 
which these motions are produced. We cannot plan these appliances 
before we know what is required for each part to do. 
What we do want, therefore, is a means of graphically repre- 
senting the various motions and actions of the machine without 
reference, in the first place, to the nature of the mechanical 
appliances by which these various motions and actions are effected. 
I have said enough I think to show that this part is most ad- 
mirably fulfilled by this system of notation, for as the designer 
plans motion after motion, and action after action, he represents 
the nature, direction, quantity, and quality of each by these 
various curved lines, and can go backwards and forwards touching 
‘up and modifying the various actions (without taxing his brain 
to carry the nature of all or any one of these actions), until he 
gets all to his satisfaction, and in proper sequence. 
(6.) The next task of the designer is that of working out the 
details of construction of the machine, and here again the system 
assists him, for he can decide from the nature of the curve on his 
chart (which curve he has before decided on to be the best 
