306
HERON OF ALEXANDRIA
the surface. He then inquires-what is the reason why the
diver is not oppressed though he has an unlimited weight of
water on his back. He accepts, therefore, the view of Ptolemy
as to the fact, however strange this may seem. But he is not
satisfied with the explanation given : * Some say ’, he goes on,
‘it is because water in itself is uniformly heavy {lao/Bapes avrb
ko.6’ avro) ’—this seems to be equivalent to Ptolemy’s dictum
that water in water has no weight—‘ but they give no ex
planation whatever why divers . . He himself attempts an
explanation based on Archimedes. It is suggested, therefore,
that Heron’s criticism is directed specifically against Ptolemy
and no one else. (4) It is suggested that the Dionysius to whom
Heron dedicated his Definitions is a certain Dionysius who
was praefectus urbi at Rome in a.d. 301. The grounds are
these (a) Heron addresses Dionysius as Aiovvcne XapLirporare,
where Xa/xnporaTos obviously corresponds to the Latin clarissi-
mus, a title which in the third century and under Diocletian
was not yet in common use. Further, this Dionysius was
curato'r aquarum and curator operum puhlicorum, so that he
was the sort of person who would have to do with the
engineers, architects and craftsmen for whom Heron wrote.
Lastly, he is mentioned in an inscription commemorating an
improvement of water supply and dedicated ‘ to Tiberinus,
father of all waters, and to the ancient inventors of marvel
lous constructions ’ (repertoribus admirabilium fabricarum
prucis viris), an expression which is not found in any other
inscription, but which recalls the sort of tribute that Heron
frequently pays to his predecessors. This identification of the
two persons named Dionysius is an ingenious conjecture, but
the evidence is not such as to make it anything more. 1
The result of the whole investigation just summarized is to
place Heron in the third century A.D., and perhaps little, if
anything, earlier than Pappus. Heiberg accepts this conclu
sion, 2 which may therefore, I suppose, be said to hold the field
for the present.
1 Dionysius was of course a very common name. Diophantus dedicated
his Arithmetica to a person of this name (rifuwTare pot Aioiwi«), whom he
praised for his ambition to learn the solutions of arithmetical problems.
This Dionysius must have lived in the second half of the third century
A. D., and if Heron also belonged to this time, is it not possible that
Heron’s Dionysius was the same person ?
2 Heron, vol. v, p. ix.