f the phonograph and
microphone, and led to their discovery. They in turn will doubtless lead
to other new inventions, which it is now impossible to foresee. We ask
in vain for an answer to the question which is upon the lips of every
one-What next? The microphone has proved itself highly useful in
strengthening the sounds given out by the telephone, and it is probable
that we shall soon see those three inventions working unitedly; for the
microphone might make the telephone sounds so powerful as to enable them
to be printed by phonograph as they are received, and thus a durable
record of telephonic messages would be obtained. We can now transmit
sound by wire, but it may yet be possible to transmit light, and see by
telegraph. We are apparently on the eve of other wonderful inventions,
and there are symptoms that before many years a great fundamental
discovery will be made, which will elucidate the connection of all the
physical forces, and will illumine the very frame-work of Nature.

In 1879, Professor Hughes endowed the scientific world with another
beautiful apparatus, his 'induction balance.' Briefly described, it
is an arrangement of coils whereby the currents inducted by a primary
circuit in the secondary are opposed to each other until they balance,
so that a telephone connected in the secondary circuit is quite silent.
Any disturbance of this delicate balance, however, say by the movement
of a coil or a metallic body in the neighbourhood of the apparatus, will
be at once reported by the induction currents in the telephone. Being
sensitive to the presence of minute masses of metal, the apparatus was
applied by Professor Graham Bell to indicate the whereabouts of the
missing bullet in the frame of President Garfield, as already mentioned,
and also by Captain McEvoy to detect the position of submerged torpedoes
or lost anchors. Professor Roberts-Austen, the Chemist to the Mint,
has also employed it with success in analysing the purity and temper
of coins; for, strange to say, the induction is affected as well by the
molecular quality as the quantity of the disturbing metal. Professor
Hughes himself has modified it for the purpose of sonometry, and the
measurement of the hearing powers.

To the same year, 1879, belong his laborious investigations on current
induction, and some ingenious plans for eliminating its effects on
telegraph and telephone circuits.

Soon after his discovery of the microphone he was invit