ver before been used on
such a gigantic piece of work, the rifling was done. After the jackets
had been shrunk on, it would be rifled again, to make it true in case
of any shrinkage.

Then came the almost Herculean task of shrinking on the great red-hot
steel jackets and wire-windings, that would add strength to the great
cannon. To do this the central core was set up on end, and the jackets,
having been heated in an immense furnace, were hoisted by a great crane
over the core, and lowered on it as one would lower his napkin ring
over the rolled up napkin.

It took weeks of hard work to do this, and Tom and Ned, with Mr. Damon
occasionally for company, remained almost constantly at the plant. But
finally the cannon was completed, the rifling was done over again to
correct any imperfections, and the manager said:

"Your cannon is completed, Mr. Swift. I want to congratulate you on it.
Never have we done such a stupendous piece of work. Only for your plans
we could not have finished it. It was too big a problem for us. Your
cannon is completed, but, of course, it will have to be mounted. What
about the carriage?"

"I have plans for that," replied Tom; "but for the present I am going
to put it on a temporary one. I want to test the gun now. It looks all
right, but whether it will shoot accurately, and for a greater distance
than any cannon has ever sent a projectile before, is yet to be seen."

"Where will you test it?"

"That is what we must decide. I don't want to take it too far from
here. Perhaps you can select a place where it would be safe to fire it,
say with a range of about thirty miles."

"Thirty miles! why, my dear sir--"

"Oh, I'm not altogether sure that it will go that distance,"
interrupted Tom, with a smile; "but I'm going to try for it, and I want
to be on the safe side. Is there such a place near here?"

"Yes, I guess we can pick one out. I'll let you know."

"Then I must get back and arrange for my powder supply," went on the
young inventor. "We'll soon test my giant cannon!"

"Bless my ear-drums!" cried Mr. Damon. "I hope nothing bursts. For if
that goes up, Tom Swift--"

"I'm not making it to burst," put in Tom, with a smile. "Don't worry.
Now, Ned, back to Shopton to get ready for the test."

CHAPTER XVI

A WARNING

"Whew, how it rains!" exclaimed Ned, as he looked out of the window.

"And it doesn't seem to show any signs of letting up," remarked Tom.
"It's been at it n