“I’ll try to show you when we have tried the phonograph test,” replied Mr. Henderson. “Ah, here’s the machine.”
Shutting off the current to the tubes, Mr. Henderson removed the sound box from the phonograph, fastened a needle to the crystal with a bit of thread and sealing wax, fastened the whole to the arm of the machine and adjusting the needle so it rested on a record set the phonograph in motion.
“Now turn on your filament rheostats,” he said, and as Tom did so, the second crystal suddenly burst into a rollicking song.
“Absolutely amazing!” declared Mr. Pauling as the record stopped.
“Here’s another!” laughed Mr. Henderson, as he again started the record moving. Then, lifting the second crystal, he placed it in his pocket with the result that he seemed to be singing himself.
The boys roared with merriment.
“Why,” cried Tom. “With one of those any one could be a ventriloquist. All you’d have to do would be to have wires leading out of sight and keep the crystal in your pocket. Wouldn’t it be rich!”
Mr. Henderson now took the singing crystal from his pocket and placed it on a bare spot of wood and to every one’s amazement it jumped and leaped about as if endowed with life.
“Dances while it sings,” remarked Mr. Henderson. “That shows how strong the vibrations are. Now let’s try the test for electricity I mentioned.”
Selecting a large crystal Mr. Henderson placed it in one of the metal frames whose use the boys could not fathom and after fastening wires to it asked if they had a voltmeter.