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If the system was used in Aria for calculations
at that early day, we may be
tolerably sure that Pythagoras would become acquainted
with it. We know that the Pythagorean
brethren, who were highly refined, exclusive,
gentlemanly, and aristocratic
people, supported themselves for centuries
by their brains, and that they possessed
some secret about numbers,— which
was kept as only trade secrets are apt to be
kept,— and which secret was of such
a nature as to lead them to speak in
concealed ways of the number ten.
Thus they called it the tetrad, a word which does
not naturally suggest ten; but ten