678 L. F. MENABREA ON BABBAGE’S ANALYTICAL ENGINE. 
tervals. The process of raising the threads is thus resolved into 
that of moving these various lever-arms in the requisite order. 
To effect this, a rectangular sheet of pasteboard is taken, some- 
what larger in size than a section of the bundle of lever-arms. 
If this sheet be applied to the base of the bundle, and an ad- 
vancing motion be then communicated to the pasteboard, this 
latter will move with it all the rods of the bundle, and conse- 
quently the threads that are connected with each of them. But if 
the pasteboard, instead of being plain, were pierced with holes 
corresponding to the extremities of the levers which meet it, then, 
since each of the levers would pass through the pasteboard 
during the motion of the latter, they would all remain in their 
places. We thus see that it is easy so to determine the posi- 
tion of the holes in the pasteboard, that, at any given moment, 
there shall be a certain number of levers, and consequently 
of parcels of threads, raised, while the rest remain where 
they were. Supposing this process is successively repeated ac- 
cording to a law indicated by the pattern to be executed, we 
perceive that this pattern may be reproduced on the stuff. For 
this purpose we need merely compose a series of cards accord- 
ing to the law required, and arrange them in suitable order one 
after the other; then, by causing them to pass over a polygonal 
beam which is so connected as to turn a new face for every 
stroke of the shuttle, which face shall then be impelled parallelly 
to itself against the bundle of lever-arms, the operation of raising 
the threads will be regularly performed. Thus we see that 
brocaded tissues may be manufactured with a precision and ra- 
pidity formerly difficult to obtain. 
Arrangements analogous to those just described have been 
introduced into the Analytical Engine. It contains two prin- 
cipal species of cards: first, Operation cards, by means of which 
the parts of the machine are so disposed as to execute any 
determinate series of operations, such as additions, subtractions, 
multiplications, and divisions; secondly, cards of the Variables, 
which indicate to the machine the columns on which the results 
are to be represented. The cards, when put in motion, success- 
ively arrange the various portions of the machine according to 
the nature of the processes that are to be effected, and the ma- | 
chine at the same time executes these processes by means of 
the various pieces of mechanism of which it is constituted. 
In order more perfectly to conceive the thing, let us select 
