climbed up and set fire to one of the
nests, and then, when they saw the whole lot going, they became
frightened and ran away."

And Tom's theory was, eventually, proved to be true. Some
lads, wandering afield, had set fire to the crows' nests and then,
frightened as they saw a bigger blaze than they intended, ran away.

Tom and Ned did not remain to see what the returning crows might think
about the destruction of their homes, provided they saw fit to return,
but, starting the aeroplane, were again on their way.

Tom had lingered long enough to make sure that his latest combination
of chemicals had been just what was needed. He felt sure that by using
a larger quantity, no fire, however fierce, could continue to blaze.

"But I want to give it a good trial, Ned, as we did from the tower,"
said Tom. "Though I don't believe there'll be a fizzle this time."

It did not take long for Tom to secure another supply of the new
chemical. He then went with it to the firm in Newmarket that was making
his containers, or "bombs" as he called them.

On his return he consulted with Mr. Baxter as to the ingredients of the
fluid that had put out the blaze in the tree.

"I believe you have at last hit on the right combination," said the
chemist. "You are on the road to success, Tom. I wish I could say the
same of myself."

"Perhaps your formulae may come back to you as suddenly as they
disappeared, or as quickly as I discovered that I had the right thing
to put out the fire," said Tom hopefully.

Busy days followed for the young inventor. Now that he was convinced he
had at last evolved the right mixture of chemicals, he prepared to make
a test on a larger scale than merely a blazing tree.

"I'll try it with a fire in the pit," he said to his chum.

Preparations were made, and the day before Tom was to carry out his
plans he received a letter.

"What's the matter? Bad news?" asked Ned, as he saw his friend's face
change after reading the epistle.

"Nothing much. Only Mary is going away, and I had expected her to be at
the test," Tom answered.

"Going away?" echoed Ned. "For long?"

"Oh, no, only for a couple of weeks. She is going to visit an uncle and
aunt in Newmarket, or just outside of that city. Another uncle, Barton
Keith, has offices in the Landmark Building, I believe."

"Landmark Building," murmured Ned. "Isn't that where Field and Melling
hang out?"

"Yes. But don't mention Mary's uncle in connection wit