the same letters, and consequently it would be easily able to write or
understand what the other desired to signify to it. The invention is
beautiful, but I do not think there can be found in the world a magnet
that has such a virtue. Neither is the thing expedient, for treason
would be too frequent and too covert."

The same idea was also indicated by Joseph Glanville in his _Scepsis
scientifica_, which appeared in 1665, by Father Le Brun, in his
_Histoire critique des pratiques superstitieuses_, and finally by the
Abbe Barthelemy in 1788.

The suggestion offered by Father Kircher, in his _Magnes sive de arte
magnetica_, is a little different from the preceding. The celebrated
Jesuit father seeks however, to do nothing more than to effect a
communication of thoughts between two rooms in the same building. He
places, at short distances from each other, two spherical vessels
carrying on their circumference the letters of the alphabet, and each
having suspended within it, from a vertical wire a magnetized figure. If
one of these latter he moved, all the others must follow its motions,
one after the other, and transmission will thus be effected from the
first vessel to the last. Father Kircher observes that it is necessary
that all the magnets shall be of the same strength, and that there shall
be a large number of them, which is something not within the reach
of everybody. This is why he points out another mode of transmitting
thought, and one which consists in supporting the figures upon vertical
revolving cylinders set in motion by one and the same cord hidden with
in the walls.

There is no need of very thoroughly examining all such systems of
magnetic telegraphy to understand that it was never possible for them to