On Babbages System of Mechanical Notation. 115 



possible for that particular purpose),* what class of motion, 

 whether crank, link motion, wheels, or cam work, he should 

 adopt, and supposing he is required to adopt the more compli- 

 cated form of cam work, the curve on the chart will enable him 

 to sketch directly, and without any calculation the shape of his cam. 



(c.) Now as to the putting together of the machine. I do not 

 mean by this, simply the reputting of the machine together after 

 it has been once completed, but I mean the putting together for 

 the first time of the various parts which have been separately 

 and disjointedly completed to scale drawings, the ascertaining 

 of the exact position in which to place each wheel, levers, and 

 cams, so that all may work properly, and each part fulfil its 

 proper duty, and at the proper time. In complicated machines, 

 this is the one operation in which above all others, workmen are 

 apt to make mistakes, for as the appliance for each motion has 

 to be placed and "keyed" independently, it is very difficult indeed 

 to say, except by a laborious tentative system of trial, whether 

 that particular motion tallies perfectly with all the other motions, 

 not only these already attached, but those to be attached. 



Here again Mr. Babbage comes to our assistance, for by 

 attaching to the main shaft of the machine (which makes one 

 revolution for each cycle), a cardboard disc divided into the same 

 number of parts as the chart, we have in keying on any par- 

 ticular motion, only to bring the shaft round till the divided disc 

 reads such a division as corresponds to some certain action 

 of that particular cam, or lever — say the commencement or end 

 of some particular action, and then turn the cam or lever on the 

 shaft until that action does actually take place, and there key 

 it, and so on through all the motions : so that really the work- 

 man might put the whole machine together, find out the position 

 for all the motions, key them on, and be perfectly satisfied in 

 his own mind, that the machine will work perfectly correctly, 

 even though he never tried it once. 



It may be said that a mathematician could describe and note 

 down the nature and quality of all these actions without reference 

 to a graphical representation. No doubt ; but in the first place 

 the mathematics required even for very simple machinery would 

 be far higher than what we can expect mechanics to be conversant 

 with, and I think we need no argument to show that a mathe- 



