96 report — 1878. 



actuated by bell-cranks, tangs, and otber similar devices commonly used 

 in shifting machinery, sometimes under the name of clutches or escape- 

 ments. These clutches and bell-cranks control the purely additive and 

 carrying processes effected in the additive trains described in the note to 

 § I., and, being themselves suitably directed, secure that the proper processes 

 shall be performed upon the proper subject-matter of operation, and duly 

 recorded, or used, as may be required. 



2. The store. — A series of columns, each containing a series of wheels, 

 constitutes the store. This store, which may be in three or more dimen- 

 sions, both receives the results of operations performed in the mill, and 

 serves as a store for the numbers which are to be used in the mill, whether 

 as original or as fresh subjects of operation in it. Each column in the 

 store corresponds to a definite number, to which it is set either automati- 

 cally or by hand, and the number of digits in this number is limited by 

 the number of wheels carried on the shaft of the column. The wheels 

 o-ear into a series of racks, which can be thrown into or out of gear by 

 means of the cards. 



3. Variable cards. — All the numbers which are the subject of operation 

 in the mill, whether they are the result of previous operations therein, or 

 new numbers to be operated upon for the first time, are introduced to it 

 in the form of Jacquard* cards, such as are used in weaving. One set of 

 wires or axes transfers the numbers on these cards to the subject of ope- 

 ration in the mill, exactly as similar cards direct which of the warp 

 threads are to be pushed up, and which down, in the Jacquard loom. The 

 mill itself punches such cards when required. 



4. Operation cards. — A different set of cards selects and prescribes the 

 sequence of operations. These act, not upon the number wheels of the 

 mill or store, but upon the cams and clutches which direct the gearing 

 of these wheels and trains. Thus, in such an operation as (a b + c) d, 

 we should require : — 



1st, 4 variable cards with the numbers a, b, c, d. 



2nd, an operation card directing the machine to multiply a and b 



together. 

 3rd, a record of the result, namely the product ab = p, as a fifth 



variable card. 

 4th, an operation card directing the addition of p and c. 

 5th, a record of the result, namely the sum p + c=q, as a 6th variable 



card, 

 6th, an operation card directing the machine to multiply ~q and d 



together. 

 7th, a record of the result, namely the product qd=p 2 , either printed 



as a final result or punched in a seventh variable card. 



* In a letter written by Mr. Babbage to Arago in December 1839, the following 

 explanation of the use of these cards is given. It probably conveys the idea in the 

 fewest words possible. It is only necessary to add that their twofold employment 

 embodies the separation of the symbols of operation from those of quantity. " You 

 are aware that the system of cards which Jacquard invented are the means by 

 which we can communicate to a very ordinary loom orders to weave any pattern 

 that may be desired. Availing myself of the same beautiful invention, I have by 

 similar means communicated to my calculating engine orders to calculate any 

 formula however complicated ; but I have also advanced one stage further, and I 

 have communicated through the same means orders to follow certain laws in the use 

 of those cards, and thus the calculating engine can solve any equations, eliminate 

 between any number of variables, and perform the highest operations of analysis." 



