interrupters?" queried Ted.

"Those current interrupters are the things which have since become
known as transmitters," explained Mr. Hazen. "Those Mr. Bell made all
alike except that in each one of them were springs kept in constant
vibration by a magnet or point of metal placed above each spring so
that the spring would touch it at every vibration, thus making and
breaking the electric current the same number of times per second that
corresponded to the pitch of the piece of steel. By tuning the springs
of the receivers to the same pitch with the transmitters and running a
wire between them equipped with signalling keys and a battery, Bell
reasoned he could send as many messages at one time as there were
pitches."

"Did he get it to work?" Laurie asked.

"Mr. Bell didn't, no," replied the tutor. "What sounded logical enough
on paper was not so easy to put into practise. The idea has been
carried out successfully, however, since then. But Mr. Bell
unfortunately had no end of troubles with his scheme, and we all may
thank these difficulties for the telephone, for had his harmonic
telegraph gone smoothly we might not and probably would not have had
Bell's other and far more important invention."

"The discovery of the telephone was a 'happen,' then," Ted ventured.

"More or less of a happen," was the reply. "Of course, the intelligent
recognition of the law behind it was not a happen; nor was the patient
and persistent toil that went into the perfecting of the instrument a
matter of chance. Alexander Graham Bell had the genius to recognize the
value and significance of the truth on which he stumbled and turn it to
practical purposes. Many another might perhaps have heard the self-same
sounds that came to him over that reach of wire and, detecting nothing
unusual in the whining vibrations, have passed them by. But to Mr. Bell
they were magic music, the sesame to a new country. Strangely enough,
too, it was the good luck of a boy not much older than Ted to share
with the discoverer the wonderful secret."

"How?" demanded both Laurie and Ted in a breath.

"I can't tell you that story to-day," Mr. Hazen expostulated. "It would
take much too long. We must give over talking and put our minds on this
telephone of our own which does not seem to be making any great
progress. I begin to be afraid we haven't the proper outfit."

As he spoke, a shadow crossed the window and in another instant Mr.
Clarence Fernald poked his