Meanwhile further investigation bad been made of clues leading to the origin of the blaze in the shed, but nothing had been learned. A photo-telephone had been installed near Eradicate's quarters, in the hope that the mysterious stranger might keep his promise, and come to see about the mule. In that case something would have been learned about him. But, as Tom feared, the man did not appear.

Just previous to the opening of this story Tom had made a peculiar instrument, described in the volume entitled "Tom Swift and His Photo-Telephone." With that a person talking could not only see the features of the person with whom he was conversing, but, by means of a selenium plate and a sort of camera, a permanent picture could be taken of the person at either end of the wire.

I've got dad half distracted trying to solve the problem, so I've had to let up on him for a while. Come on out and see what you make of it." "Sure, Tom, anything to oblige. If you want me to sit in front of your photo-telephone, and have my picture taken, I'm agreeable, even if you shoot off a flashlight at my ear.

Following this achievement Tom invented a wizard camera and a great searchlight, which, with his giant cannon, was purchased by the United States Government. Work on his photo-telephone and his aerial warship, the problem of digging a big tunnel, and then traveling to the land of wonders, kept Tom Swift very busy, and he had just completed a wonderful piece of work when the present story opens.

From one activity to another had Tom Swift gone, now constructing some important invention for himself, as among others, when he made the photo-telephone, or developed a great searchlight which he presented to the Government for use in detecting smugglers on the border.

I'll just rig up one of my photo-telephone machines, so that, if he does come to have a talk with Rad, we can both see and hear him." "That's great, Tom! But do you think this fellow had anything to do with the fire?" "I don't know. He knew about it, of course. This isn't the first fire we've had in the works, and, though we always fight them ourselves, still news of it will leak out to the town.

He helped dig a big tunnel, he constructed a photo-telephone, a great searchlight and a monster cannon. Occasionally he had searched for treasure, once under the sea, with considerable success. Of late his and his father's industries had become so important that a number of new buildings had been constructed and the plant greatly enlarged.