“Yes, I’ve often seen that.”

“Well then, ‘bless my watch chain!’ as Mr. Damon would say, I think I’ve got just what I want.  I’m going to try a wet plate now, and I think it will work.  Come on now.  Speed up!  I’m in a great big hurry to get home and try it!”

“Well, Tom, I sure will be glad if you’ve got the right idea,” laughed Ned.  “It will be worth getting wet through for, if you strike something.  Good luck!”

Tom could hardly wait to fasten up his boat for the night, so eager was he to get to his shop laboratory and try the new idea.  A gleam of hope had come to him.

It was still early evening, and Tom, when enticed out by Ned, had left his photo telephone apparatus in readiness to go on with his trials as soon as he should have come back.

“Now for it, Ned!” exclaimed the young inventor, as he took off his coat.  “First I’ll sensitize a selenium plate, and then I’ll wet it.  Water is always a good conductor of electricity, and it’s a wonder that I forgot that when I was planning this photo telephone.  But seeing the sparkle of lights, and the reflection of ourselves in the lake to-night, brought it back to me.  Now then, you haven’t anything special to do; have you?”

“Not a thing, Tom.”

“That’s good.  Then you get in this other telephone closet—­the one in the casting shop.  I’ll put a prepared plate in there, and one in the booth where I’m to sit.  Then I’ll switch on the current, and we’ll see if I can make you out, and you notice whether my image appears on your plate.”

It took some little time to make ready for this new test.  Tom was filled with enthusiasm, and he was sure it was going to be successful this time.  Ned watched him prepare the selenium plates —­plates that were so sensitive to illumination that, in the dark, the metal would hardly transmit a current of electricity, but in the light would do so readily, its conductivity depending on the amount of light it received.

“There, I guess we’re all ready, Ned,” announced Tom, at last.  “Now you go to your little coop, and I’ll shut myself up in mine.  We can talk over the telephone.”

Seated in the little booth in one of the smaller of Tom’s shops, Ned proceeded with his part in the new experiment.  A small shelf had been fitted up in the booth, or closet, and on this was the apparatus, consisting of a portable telephone set, and a small box, in which was set a selenium plate.  This plate had been wet by a spray of water in order to test Tom’s new theory.

In a similar booth, several hundred feet away, and in another building, Tom took his place.  The two booths were connected by wires, and in each one was an electric light.

“All ready, Ned?” asked Tom, through the telephone.

“All ready,” came the answer.

“Now then, turn on your switch—­the one I showed you—­and look right at the sensitized plate.  Then turn out your light, and slowly turn it on.  It’s a new kind, and the light comes up gradually, like gas or an oil lamp.  Turn it on easily.”