“By Jove, Tom!” the lad exclaimed in a tense whisper.  “If it isn’t that Eckert fellow I’m a cow.”

“That’s what I thought,” spoke Tom coolly.  “Not that you’re a cow, Ned, but I believe that this man is one of the moving picture partners, who are rivals of Mr. Period.  I wasn’t quite sure myself after the first glance I had of him, so I wanted you to take a look.  Do you know the other chap—­the one who ran out when I asked for my telegram?”

“No, I’ve never seen him before as far as I know.”

“Same here.  Come on.”

“What are you going to do?”

“Go back to the airship, and tell Mr. Nestor.  As one of the directors in the concern I’m working for.  I want his advice.”

“Good idea,” replied Ned, and they turned to leave the office.  The spying stranger, and William Eckert, were not in sight when the two lads came out.

“They got away mighty quick,” remarked Tom, as he looked up and down the street.

“Yes, they probably saw us turn to come out, and made a quick get-away.  They might be in any one of these places along here,” for the street, on either side of the telegraph office, contained a number of hotels, with doors opening on the sidewalk.

“They must be on your trail yet,” decided Mr. Nestor when Tom, reaching the anchored airship, told what had happened.  “Well, my advice is to go to Africa as soon as we can.  In that way we’ll leave them behind, and they won’t have any chance to get your camera.”

“But what I can’t understand,” said Tom, “is how they knew I was coming here.  It was just as if that one man had been waiting in the telegraph office for me to appear.  I’m sorry, now, that I mentioned to Ned where we were ordered to.  But I didn’t think.”

“They probably knew, anyway,” was Mr. Nestor’s opinion.  “I think this may explain it.  The rival concern in New York has been keeping track of Mr. Period’s movements.  Probably they have a paid spy who may be in his employ.  They knew when he sent you a telegram, what it contained, and where it was directed to.  Then, of course, they knew you would call here for it.  What they did not know was when you would come, and so they had to wait.  That one spy was on guard, and, as soon as you came, he went and summoned Eckert, who was waiting somewhere in the neighborhood.”

“Bless my detective story!” cried Mr. Damon.  “What a state of affairs!  They ought to be arrested, Tom.”

“It would be useless,” said Mr. Nestor.  “They are probably far enough away by this time.  Or else they have put others on Tom’s track.”

“I’ll fight my own battles!” exclaimed the young inventor.  “I don’t go much on the police in a case like this, especially foreign police.  Well, my camera is all right, so far,” he went on, as he took a look at it, in the compartment where he kept it.  “Some one must always remain near it, after this.  But we’ll soon start for Africa, to get some pictures of a native battle.  I hope it isn’t the red pygmies we have to photograph.”