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they were so placed as to assist in the ob-
servation of the heliacal risings [4] of cer-
tain stars. If the star were known, this
would give an approximate date. Up to the
present the results of these investigations
are far from being conclusive.
Ptolemy (130 A.D.) wrote the Suntaxis,
or Almagest, which includes a cyclopedia of
astronomy, containing a summary of knowl-
111
