lection.

"That laugh will do him more good than medicine," declared the doctor,
as he took his leave. "I'll come again, when I can make a more thorough
examination," he added.

For Tom the following days, that lengthened into weeks, were anxious
ones. There was a constant worry over Eradicate. Then, too, he was
having trouble with his latest invention--his aerial fire-fighting
apparatus. It was not that Tom was financially dependent on this
invention. He was wealthy enough for his needs from other patented
inventions he and his father owned.

But Tom Swift was a lad not easily satisfied. Once embarked on an
enterprise, whether it was the creation of a gigantic searchlight, an
electric rifle, a photo telephone or a war tank, he never rested until
he had brought it to a successful consummation.

But there was something about this chemical fire extinguishing mixture
that defied the young inventor's best efforts. Mixture after mixture
was tried and discarded. Tom wanted something better than the usual
carbonate and sulphuric combination, and he was not going to rest until
he found it.

"I think you've struck a blind lead, Tom," said Ned, more than once.

"Well, I'm not going to give up," was the firm answer.

"Bless my shoe laces!" cried Mr. Damon, when he had called on Tom once
at the Baxter laboratory and had been driven out, holding his breath,
because of the chemical fumes, "I should think you couldn't even start
a fire with that around, Tom, much less need to put one out."

"Well, it doesn't seem to work," said the young inventor ruefully.
"Everything I do lately goes wrong."

"It is that way sometimes," said Mr. Baxter. "Suppose you let me study
over your formulae a bit, Mr. Swift. I haven't given much thought to
fire extinguishers, but I may be able, for that very reason, to
approach the subject from a new angle. I'll lay aside my attempt to get
back the lost formulae and help you."

"I wish you would!" exclaimed Tom eagerly. "My head is woozie from
thinking! Suppose I leave you to yourself for a time, Mr. Baxter? I'll
go for an airship ride."

"Yes, do," urged the chemist. "Sometimes a change of scene is of
benefit. I'll see what I can do for you."

"Will you come along, Ned--Mr. Damon?" asked Tom, as he prepared to
leave the improvised laboratory, the repairs on his own not yet having
been finished.

"Thank you, no," answered Ned. "I have some collections to make."

"And I promised my wife I'd ta