ST6 Mr Babbage on Maclimety for Calculating 
equal in speed to the writer. At another trial, thirty 4wo num- 
bers of the same table were calculated in two minutes amd thirty 
seconds ; and, as these contained eighty-tivo figures, the engine 
produced thirty-three every minute. Another time it produced 
forty four figures in a minute ; and, as the machine may be 
moved uniformly by a weight, this “rate of computation may be 
maintained for any length of time ; and it is probable that few 
writers are able to copy, with equal speed, for many hours to- 
gether. 
Nothwithstanding the defective workmanship in this first ma- 
chine, its computations are wonderfully accurate ; and some very 
skilful mechanics to whom Mr Babbage has shewn it in confi- 
dence, are of opinion that it may be carried to any extent. Its 
parts, indeed, are few, but frequently repeated ; and, though it 
contains many wheels, yet only a few of them move at the same 
time, so that its simplicity is greater than that of many machines 
in common and constant use. 
There is one circumstance in the construction of this machine, 
which is of considerable importance in making larger ones, viz. 
that, though its wheels are numerous, yet, by a peculiar contri- 
vance, any error produced by accident, or by a slight inaccuracy 
in one of them, is corrected as soon as it is transmitted to the next, 
and in such a manner as effectually to prevent any accumulation 
of small errors from producing a wrong figure in the Calculation. 
The machine for composing with types, has not yet been ac- 
tually constructed ; but, from several models which Mr Babbage 
has made, and from numerous experiments which he has tried, 
there can be no doubt of its complete success When put up, 
the composing machine will contain about 30,000 types, which 
are put in their places by children ; but the person who attends 
the engine has a method of ascertaining, in less than half an 
hour, f any one individual cf this number is misplaced. 
As the engine for computing tables by the method of differ- 
ences, is the only one which Mr Babbage has yet completed, he 
has, in his letter to Sir Humphry Davy, confined himself, to a 
statement of the powers which that method possesses, and as this 
statement is highly interesting, we shall give it in his own words. 
• A working-model of this part of the machinery has been recently constructed^ 
