“There are no disks or cylinders of wax, as in the phonograph, but two large spools of extremely fine steel wire.  The record is not made mechanically on a cylinder, but electromagnetically on this wire.  Small portions of magnetism are imparted to fractions of the steel wire as it passes between two carbon electric magnets.  Each impression represents a sound wave.  There is no apparent difference in the wire, no surface abrasion or other change, yet each particle of steel undergoes an electromagnetic transformation by which the sound is indelibly imprinted on it until it is wiped out by the erasing magnet.  There are no cylinders to be shaved; all that is needed to use the wire again is to pass a magnet over it, automatically erasing any previous record that you do not wish to preserve.  You can dictate into it, or, with this plug in, you can record a telephone conversation on it.  Even rust or other deterioration of the steel wire by time will not affect this electromagnetic registry of sound.  It can be read as long as steel will last.  It is as effective for long distances as for short, and there is wire enough on one of these spools for thirty minutes of uninterrupted record.”

Craig continued to tinker tantalisingly with the machine.

“The principle on which it is based,” he added, “is that a mass of tempered steel may be impressed with and will retain magnetic fluxes varying in density and in sign in adjacent portions of its mass.  There are no indentations on the wire or the steel disk.  Instead there is a deposit of magnetic impulse on the wire, which is made by connecting up an ordinary telephone transmitter with the electromagnets and talking through the coil.  The disturbance set up in the coils by the vibration of the diaphragm of the transmitter causes a deposit of magnetic impulse on the wire, the coils being connected with dry batteries.  When the wire is again run past these coils, with a receiver such as I have here in circuit with the coils, a light vibration is set up in the receiver diaphragm which reproduces the sound of speech.”

He turned a switch and placed an ear-piece over his head, giving me another connected with it.  We listened eagerly.  There were no foreign noises in the machine, no grating or thumping sounds, as he controlled the running off of the steel wire by means of a foot-pedal.

We were listening to everything that had been said over the Willoughby telephone during the day.  Several local calls to tradesmen came first, and these we passed over quickly.  Finally we heard the following conversation: 

“Hello.  Is that you, Ella?  Yes, this is Maud.  Good-morning.  How do you feel to-day?”

“Good-morning, Maud.  I don’t feel very well.  I have a splitting headache.”

“Oh, that’s too bad, dear.  What are you doing for it?”

“Nothing—­yet.  If it doesn’t get better I shall have Mr. Willoughby call up Dr. Guthrie.”