702 TRANSLATOR’S NOTES TO M. MENABREA’S MEMOIR 
which the whole mass of its mechanism will assume is not yet finally 
determined. 
We may conveniently represent the columns of dises on paper in a 
diagram like the following :— 
The V’s are for the purpose of convenient reference 
A Ss O 3 ik to any column, either in writing or speaking, and 
on OO * are consequently numbered. ‘The reason why the 
letter V is chosen for this purpose in preference to 
0 30 "0 : 
‘ee ae &e. any cther letter, is because these columns are de- 
0000 signated (as the reader will find in proceeding with 
ft an ke the Memoir) the Variables, and sometimes the 
Variable columns, or the columns of Variables. ‘The 
origin of this appellation is, that the values on the columns are destined 
to change, that is to vary, in every conceivable manner. But it is 
necessary to guard against the natural misapprehension that the co- 
lumns are only intended to receive the values of the variables in an 
analytical formula, and not of the constants. The columns are called 
Variables on a ground wholly unconnected with the analytical distine- 
tion between constants and variables. In order to prevent the possi- 
bility of confusion, we have, both in the translation and in the notes, 
written Variable with a capital letter when we use the word to signify 
a column of the engine, and variable with a small letter when we mean 
the variable of a formula. Similarly, Variable-cards signify any cards 
that belong to a column of the engine. 
To return to the explanation of the diagram: each circle at the top 
is intended to contain the algebraic sign + or —, either of which can 
be substituted * for the other, according as the number represented on 
the column below is positive or negative. In a similar manner any 
other purely symbolical results of algebraical processes might be made 
to appear in these cireles. In Note A. the practicability of developing 
symbolical with no less ease than numerical results has been touched on. 
The zeros beneath the symbolic circles represent each of them a dise, 
supposed to have the digit 0 presented in front. Only four tiers of 
zeros have been figured in the diagram, but these may be considered 
as representing thirty or forty, or any number of tiers of discs that 
may be required. Since each dise can present any digit, and each 
circle any sign, the dises of every column may be so adjusted} as to 
express any positive or negative number whatever within the limits of 
the machine ; which limits depend on the perpendicular extent of the 
mechanism, that is, on the number of dises to a column. 
* A fuller account of the manner in which the signs are regulated, is given 
in Mons. Menabrea’s Memoir, pages 682, 683. He himself expresses doubts 
(in a note of his own at the bottom of the latter page) as to his having been 
likely to hit on the precise methods really adopted; his explanation being 
merely a conjectural one. That it does accord precisely with the fact is a 
remarkable circumstance, and affords a convincing proof how completely Mons. 
Menabrea has been imbued with the true spirit of the invention. Indeed the 
whole of the above Memoir is a striking production, when we consider that 
Mons. Menabrea had had but very slight means for obtaining any adequate 
ideas respecting the Analytical Engine. It requires however a considerable 
acquaintance with the abstruse and complicated nature of such a subject, in’ 
order fully to appreciate the penetration of the writer who could take so just | 
and comprehensive a view of it upon such limited opportunity. b 
+ This adjustment is done by hand merely. H 
