386 Analyses of Books, = [Nov. 
rather more than kept pace with the engine ; but as soonas four 
figures were required, the machine was at least equal in speed 
to the writer. rrolatis 
‘< In another trial it was found that 30 numbers of the same 
table were calculated in two minutes and thirty seconds: as 
these contained 82 figures, the engine produced 33 every 
minute. 
“In another trial it produced figures at the rate of 44 in a 
minute. .As the machine may be made to move uniformly by a 
weight, this rate might be maintained for any length of time, 
and I believe few writers would be found to copy with equal 
speed for many hours together. Imperfect as a first machine 
generally is, and suffering as this particular one does from great 
defect in the workmanship, I have every reason to be satisfied 
with the accuracy of its computations ; and by the few skilful 
mechanics to whom I have in confidence shown it, I am assured 
that its principles are such that it may be carried to any extent. 
In fact, the parts of which it consists are few but frequently 
repeated, resembling in this respect the arithmetic to which it is 
applied, which, by the aid of a few digits often repeated, pro- 
duces all the wide variety of number. The wheels of which it 
consists are numerous, but few move at the same time; and I 
have employed a principle by which any small error that may 
arise from accident or bad workmanship is corrected as soon as 
it is produced, in such a manner as effectually to prevent any 
accumulation of small errors from producing a wrong figure in 
the calculation. 
“ Of those contrivances by which the composition is to be 
effected, I have made many experiments and several models ; the 
results of these leave me no reason to doubt of success, which is 
still further confirmed by a working model that is just finished.” 
A method of determining the existence of error, should it by 
possibility arise in any page that the engine has composed, is 
also mentioned ; with a few of the variety of tables which could 
be calculated by that actually constructed. ‘ The tables of 
powers and products published at the expense of the Board of 
Longitude, and calculated by Dr. Hutton, were solely executed 
by the method of differences; and other tables of the roots of 
numbers have been calculated by the same gentlemen on similar 
principles.” 
In order to show the mental labour that may be saved by the 
employment of his machine, Mr. Babbage describes the course 
which was pursued, in the formation of the tables computed 
under the direction of M. Prony by order of the French govern- 
ment, constituting one of the most stupendous monuments of 
arithmetical calculation which the world has yet produced, and 
occupying 17 large folio volumes. This enormous mass of com- 
putation, one table of which must contain about eight millions of 
figures, was executed by three sections of calculators. The first 
