And, when his chum came in, Tom cried: 

“Ned, what do you think?  I know who had my airship!”

“How?” asked Ned, in wonder.

“By that button clue!  Yes, it’s the same kind—­they’re as alike as twins!” and Tom brought out the button which he had put away in his desk.  “See, Boylan had one just like this on the back of his coat.  The other was missing.  Here it is—­it was in the seat of my airship, where it was probably pulled off as he moved about.  Ned, I think I’ve got the right clue at last.”

Ned said nothing for several seconds.  Then he remarked slowly: 

“Well, Tom, it proves one thing; but not the other.”

“What do you mean?”

“I mean that it may be perfectly true that the button came off Mr. Boylan’s coat, but that doesn’t prove that he wore it.  You can be reasonably sure that the coat was having a ride in your Eagle, but was Boylan in the coat?  That’s the question.”

“In the coat?  Of course he was in it!” cried Tom.

“You can’t be sure.  Someone may have borrowed his coat to take a midnight ride in the airship.”

“Mr. Boylan doesn’t look to be the kind of a man who would lend his clothes,” remarked Tom.

“You never can tell.  Someone may have borrowed it without his knowledge.  You’d better go a bit slow, Tom.”

“Well, maybe I had.  But it’s a clue, anyhow.”

Ned agreed to this.

“And all I’ve got to do is to find out who was in the coat when it was riding about in my airship,” went on Tom.

“Yes,” said Ned, “and then maybe you’ll have some clue to the disappearance of Mr. Damon.”

“Right you are!  Come on, let’s get busy!”

“As if we hadn’t been busy all the while!” laughed Ned.  “I’ll lose my place at the bank if I don’t get back soon.”

“Oh, stay a little longer—­a few days,” urged Tom.  “I’m sure that something is going to happen soon.  Anyhow my photo telephone is about perfected.  But I’ve just thought of another improvement.”

“What is it?”

“I’m going to arrange a sort of dictaphone, or phonograph, so I can get a permanent record of what a person says over the wire, as well as get a picture of him saying it.  Then everything will be complete.  This last won’t be hard to do, as there are several machines on the market now, for preserving a record of telephone conversations.  I’ll make mine a bit different, though.”

“Tom, is there any limit to what you’re going to do?” asked Ned, admiringly.

“Oh, yes, I’m going to stop soon, and retire,” laughed the young inventor.

After talking the matter over, Tom and his chum decided to wait a day or so before taking any action in regard to the button clue to the takers of the airship.  After all, no great harm had been done, and Tom was more anxious to locate Mr. Damon, and try to get back his fortune, as well as to perfect his photo telephone, than he was to discover those who had helped themselves to the Eagle.