During the retreat of the Ten Thousand a cutting north-
wind blew in the faces of the soldiers ; sacrifices were offered
to Boreas, and the severity of the wind immediately ceased,
which seemed a proof of the god's causation, [p.]

13. What method is employed in the following ?

** Brewster accidentally took an impression from a piece
of mother-of-pearl in a cement of resin and bees' wax, and
finding the colours repeated upon the surface of the wax,
proceeded to take other impressions in balsam, fusible
metal, lead, gum-arabic, &c., and always found the iri-
descent colours the same. He thus proved that the chemical
nature is wholly a matter of indifference, and the form of
the surface is the condition of such colours."



XXIX.] AND PROBLEMS. 293

14. What is the difference, logically, between the sen-
tences : — Leibnitz, a great philosopher, has said, &a j and
A great philosopher, Liebnitz, has said, &c. ? [c]

15. What is successive induction, or induction by con-
nection, as in the proof that «« =1-1-3+5-1-

up to n of the odd numbers ? [h.]

(See Elementary Lessons in Logic, lesson xxvi. p. 220.)

16. Give an inductive proof that ^ - a" is divisible by
X - a, when « is a whole number.
