wood, the
weight will be thirty pounds per cubic foot, and as all the boards will
take fourteen cubic feet of lumber, the total weight, including the
posts, can be brought within 450 pounds, and I do not think our other
material will weigh much over 500 more."

"That would not be a hard load," observed the Professor, "as we have
often hauled a ton, but it would be well to make a new set of wheels,
and we can then take with us an extra wheel for the front and rear."

"I think we should take tools along also," said Tom, "because we can
always make our own repairs, in that event."

"I am glad you referred to that. It is certainly a suggestion in the
right direction. Are there any more observations from any of the other
army engineers?"

"I may be wrong," answered Harry, "but it seems to me that one of the
folding fences should be put on each side of the wagon body, and the
third under the wagon."

"What is your reason for that?" asked Tom.

"Because we may want to put up the fort in a big hurry some time, and by
having them at the three places, and have it understood who are to take
out each section, it would be the work of a few moments only to set it
up, because each set of workers could handle his section without
interference from the others."

"That is really a stroke of genius. Certainly, that is the sensible
way," responded John.

"It is simply another illustration," added the Professor, "how men,
looking at things from different standpoints, will see the defects in
each other's work. That is the story of every great invention."

These conferences were of the greatest value to the boys. It pointed out
how men, through force of circumstances, were compelled to devise things
for their need.

George had been an intent listener during these discussions. "It does
seem that the old statement, 'that necessity is the mother of
invention,' is true."

The Professor turned to him smilingly, as he replied: "That may be so in
very many eases, it is true, but I imagine that in the vast majority of
instances the necessity was in the mind of the inventor to get some
money. The thought of that requirement was a more vivid thing to him
than the real need of the article as an economic necessity."

"Do you really think that is the case?"

"If my memory is not at fault, the people of England howled with
derision when the first locomotive was built; the men who put out the
first sewing machine had their stores broken into