L. F. MENABREA ON BABBAGE’S ANALYTICAL ENGINE. 671 
some of his views on this subject during a visit he made at Turin, 
I have, with his approbation, thrown together the impressions 
they have left on my mind. But the reader must not expect 
to find a description of Mr. Babbage’s engine; the comprehen- 
sion of this would entail studies of much length; and I shall 
endeavour merely to give an insight into the end proposed, and 
to develope the principles on which its attainment depends. 
I must first premise that this engine is entirely different from 
that of which there is a notice in the ‘ Treatise on the Giconomy 
of Machinery,’ by the same author. But as the latter gave rise* 
to the idea of the engine in question, I consider it will be a useful 
preliminary briefly to recall what were Mr. Babbage’s first essays, 
and also the circumstances in which they originated. 
It is well known that the French government, wishing to 
promote the extension of the decimal system, had ordered the 
construction of logarithmical and trigonometrical tables of enor- 
mous extent. M. de Prony, who had been entrusted with the 
direction of this undertaking, divided it into three sections, to 
each of which were appointed a special class of persons. In 
the first section the formulz were so combined as to render them 
subservient to the purposes of numerical calculation; in the 
second, these same formule were calculated for values of the 
variable, selected at certain successive distances ; and under the 
third section, comprising about eighty individuals, who were 
most of them only acquainted with the two first rules of arith- 
metic, the values which were intermediate to those calculated 
by the second section were interpolated by means of simple 
_ additions and subtractions. 
An undertaking similar to that just mentioned having been 
entered upon in England, Mr. Babbage conceived that the 
operations performed under the third section might be executed 
by amachine ; and this idea he realized by means of mechanism, 
* The idea that the one engine is the offspring and has grown out of the 
other, is an exceedingly natural and plausible supposition, until reflection re- 
minds us that no necessary sequence and connexion need exist between two 
such inventions, and that they may be wholly independent. M. Menabrea has 
shared this idea in common with persons who have not his profound and accu- 
rate insight into the nature of either engine. In Note A. (see the Notes at the 
end of the Memoir) it will be found sufficiently explained, however, that this 
supposition is unfounded. M. Menabrea’s opportunities were by no means such 
as could be adequate to afford him information on a point like this, which 
would be naturally and almost unconsciously assumed, and would searcely sug- 
gest any inquiry with reference to it—Note sy TRANSLATOR. 
VOL. III. PART XII. Og 
