d. $25 to
first, $10 to second, $5 to third, and $1 each to next ten. Write words
one below another, and number them. Put your own name and address at top
of sheet. Post lists not later than November 25, 1895, to HARPER'S ROUND
TABLE, New York.

Lunar Attraction.

Jacques Ozanam, the famous French mathematician, invented this
startling illusion, which I will describe for the benefit of the
Round Table.

Make a box three feet square, or of any convenient size, and place
a board of the same dimensions in the bottom, slightly inclined,
with a serpentine groove in it, so that a ball of lead can roll in
it freely. Extend a plain mirror from the elevated end of the
board to the opposite upper corner, with the reflecting side down.
Cut a small hole in the end of the box facing the mirror, and in
such a position that the grooved board itself cannot be seen. If a
ball of lead rolls along the groove, it will appear to ascend.

VINCENT V. M. BEEDE.

For Lovers of Figures.

Here are two ingenious problems, of French origin, which mathematically
inclined members will enjoy:

1. Fifteen Christians and fifteen Turks were at sea in the same vessel
when a dreadful storm came on which obliged them to throw all their
merchandise overboard. This, however, not being sufficient to lighten
the ship, the captain informed them there was no possibility of its
being saved unless half the passengers were thrown overboard also. He
therefore arranged the thirty in a row, and by counting from nine to
nine, and throwing every ninth person into the sea, beginning again at
the first of the row when it had been counted to the end, it was found
that after fifteen persons had been thrown overboard, the fifteen
Christians remained. How did the captain arrange these thirty persons so
as to save the Christians?

KEY.--The method may be deduced from this Latin sentence:

_Populeam virgam mater regina ferebat._ Or from this French couplet:

_Mort, tu ne failliras pas,_
_En me livrant le trepas._

2. Three gentlemen and their valets desiring to cross a river find a
boat without a boatman; the boat is so small that it can contain no more
than two of them at once. None of the masters can endure the valets of
the other two, and if any one of them were left with any of the other
valets, he would infallibly cane them. How can these six persons cross
the river, two and two, so