Sherefeddin only says (l. iii. c. 13) that the
rays of the setting, and those of the rising sun, were
scarcely separated by any interval; a problem which may be
solved in the latitude of Moscow (the 56th degree), with
the aid of the Aurora Borealis, and a long summer twilight.
But a day of forty days (Khondemir apud D'Herbelot, p. 880)
would rigorously confine us within the polar circle.