P. HISTORY OF ' AATHEMATICAL - School of Mathematics

246 A HISTORY OF MATHEMATICAL NOTATIONS
by De Witt.' Wallis2 wrote n for + or -, and 8 for the contrary.
The sign 8 was used in a restricted way, by James Berno~lli;~ he
says, "8 significat + in pr. e - in post. hypoth.," i.e., the symbol
stood for + according to the first hypothesis, and for -, according to
the second hypothesis. He used this same symbol in his Ars conjectandi
(1713), page 264. Van Schooten wrote also n for T. It
should be added that n appears also in the older printed Greek books
as a ligature or combination of two Greek letters, the omicron o and
the upsilon u. The n appears also as an astronomical symbol for the
constellation Taurus.
Da Cunha4 introduced +' and +', or f' and T', to mean that
the upper signs shall be taken simultaneously in both or the lower
signs shall be taken simultaneously in both. Oliver, Wait, and Jones5
denoted positive or negative N by 'N.
211. The symbol [a] was introduced by Kroneckere to represent
0 or +1 or - 1, according as a was 0 or +1 or -1. The symbol "sgn"
has been used by some recent writers, as, for instance, PeanoJ7 Netto,*
and Le Vavasseur, in a manner like this: "sgn A = + 1" when A >O,
"egn A= -1" when A