_To make any Pen-knife out of three jump out of a Goblet, agreeable
to the Option of the Company._
Take a silver goblet, as, on account of its opacity, it will hide the
means you will employ to make the pen-knife jump out at the desire of
the assembly.
This operation consists in a small spring, about an inch broad, by two
inches and a quarter long.
You are to take care to subject or bend this spring before you begin
the trick with a little bit of sugar, which being compressed between
the two ends of the spring, will prevent it from unbending.
Then ask the company, shewing your three pen-knives of different
colours, which of them they chuse to see jump out of the goblet.
Put afterwards your three pen-knives in the goblet, taking care to lay
the end of the handle of the chosen pen-knife in a little round hole
that is in the upper end of the spring, confined by the bit of sugar;
and before you withdraw your hand from the goblet, which must contain
in the bottom some drops of water, take a little of it with the tip of
your finger, and put it dexterously on the sugar, which by melting will
leave the spring at liberty to extend and make the pen-knife jump out.
While the sugar is melting, you may stand far from the goblet, and
command the pen-knife to jump out; and this will be done to the great
astonishment of the spectators. Yet nothing is so simple as the means
to make this experiment succeed, without the least assistance from any
confederate.
N. B. These little springs, fit for use, may be had of Mr. PINETTI,
Hay-Market.