Making 20

_A person having an even Number of Shillings in one Hand, and an odd
Number in the other, to tell in which hand the odd or even Number is._

You desire the person to multiply the number in his right hand by an
odd figure, and the number in his left by an even one; and tell you if
the products, added together, be odd or even. If even, the even number
is in the right hand; if odd, the even number is in the left. For
instance,

I. Number in the right In the left hand _odd_ 7
hand is _even_ 18 Multiply by 2
Multiply by 3 ----
---- Product 14
Product 54 ----
Add the Product of
the left hand 14
----
Which produces a
total of 68

II. Number in the right In the left hand _even_ 18
hand is _odd_ 7 Multiply by 2
Multiply by 3 ----
---- Product 36
Product 21
Add the Product of
the left hand 36
----
Which produces a
total of 57

_Secret Correspondence._

[Illustration: Fig. 1.]

To carry on a correspondence without the possibility of the meaning of
the letter being detected, in case it should be opened by any other
person, has employed the ingenuity of many. No method will be found
more effectual for this purpose, or more easy, than the following.

Provide a piece of square card or pasteboard, and draw a circle on it,
which circle is to be divided into 27 equal parts, in each of which
parts must be written _one_ of the capital letters of the alphabet,
and the &, as in the figure. Let the centre of this circle be blank.
Then draw another circle, also divided into 27 equal parts, in each of
which write one of the small letters of the alphabet, and the &. This
circle must be cut round, and made exactly to fit the blank space in
the centre of the large circle, and must run round a pivot or pin. The
person with whom you correspond must have a similar dial, and at the
beginning of your letter you must put the capital letter, and at the
end the small letter, which answer to each other when you have fixed
your di