Lawrence!"

"I should think it was the affair of any person who wanted to see fair
play," answered the shipowner's son.

"Nat, you take your handkerchief and wipe off Mr. Potts's clothes," said
Dave, sternly.

"Eh?" queried the money-lender's son in dismay.

"You heard what I said. Go and do it, and be quick about it."

"I--er--I don't have to."

"Yes, you do. If you don't----" Dave ended by walking over to a barrel
and filling the syringe with the spraying fluid.

"Hi! don't you douse me with that!" yelled the other youth in alarm.
Then he started to run away, but the senator's son caught him by one arm
and Phil caught him by the other.

"You've got no right to hold me!"

"Well, we'll take the right," said Roger, calmly. "Now, Nat, do as Dave
told you."

There was no help for it, and with very bad grace the money-lender's son
drew from his pocket a silk handkerchief and removed what he could of
the fluid from Caspar Potts's clothing. Many spots remained.

"I am afraid the suit is ruined," said the aged professor, sorrowfully.
"Anyway, it will need a thorough cleaning."

"If it is ruined, Nat can pay for it," said Dave, firmly.

"I'll pay for nothing!" grumbled the boy who had done the mischief. He
was short of spending-money, and knew how hard it was to get an extra
dollar from his parent.

"He certainly ought to pay for it," said Caspar Potts. "Some men would
have him locked up for what he has done."

"Humph! Don't talk foolish! It was only a little fun!" grumbled Nat. "I
didn't mean any harm. You can easily get those spots out of your
clothes."

"Did he do anything else to you?" asked Dave of the professor.

"Yes, he plagued me a good deal, and he shoved me down in the cow-yard,"
was the reply. "I was hoping some one would come to drive him away. I
said I'd have the law on him, but he laughed at me, and said nobody else
was around and his word was as good as mine."

"If that isn't Nat to a T!" murmured the senator's son. "Doing the sneak
act every time!"

"Well, we are witnesses against him," put in Phil. He looked at Dave and
suddenly began to grin. "Oh, but this is great!" he cried.

"What's struck you?" queried Dave.

"Oh, nothing, only I reckon we've got a good hold on Mr. Aaron Poole
now--in case he tries to make a complaint against you."

"To be sure we have!" burst out Roger. "He won't dare to do it--after he
knows what Professor Potts can do."

"What are you talking about?" dema