’s in M, Menabrea’s tables of [pages 16], [19], since it does not alter anything therein represented by him, but merely adds something to the previous indications of those tables. The lower indices are obviously indices of locality only, and are wholly independent of the operations performed or of the results obtained, their value continuing unchanged during the performance of calculations. The upper indices, however, are of a different nature. Their office is to indicate any alteration in the value which a Variable represents; and they are of course liable to changes during the processes of a calculation. Whenever a Variable has only zeros upon it, it is called
; the moment a value appears on it (whether that value be placed there arbitrarily, or appears in the natural course of a calculation), it becomes
. If this value gives place to another value, the Variable becomes
, and so forth. Whenever a value again gives place to zero, the Variable again becomes
, even if it have been
