Once this had been done, and Tom had figured just how much
force could be expected to be taken up by a larger check, with
stronger hydrostatic valves, the young inventor explained:

"And now to see how much recoil force my guns develop!"

"Are you really going to fire the guns?" asked Ned.

"Surely," answered Tom. "That's the only way to get at real
results. I'll have the guns taken out and mounted in a big field.
Then we'll fire them, and measure the recoil."

"Well, that may be some fun," spoke Ned, with a grin. "More fun
than all these figures," and he looked at the mass of details on
Tom's desk.

This was the second or third day after the fire in the red
shed, and in the interim Tom had been busy making computations.
These were about finished. Meanwhile further investigation bad
been made of clues leading to the origin of the blaze in the
shed, but nothing had been learned.

A photo-telephone had been installed near Eradicate's quarters,
in the hope that the mysterious stranger might keep his promise,
and come to see about the mule. In that case something would have
been learned about him. But, as Tom feared, the man did not
appear.

Ned was much interested in the guns, and, a little later, he