Fig. 10. The First Gun
"It would be well," said the Professor, "to polish the inside of the bored barrels, and thus make a much better weapon."
"How can we do this?" asked Harry.
"There are several ways, but the better plan would be to take a good polishing material, in the form of a fine sand or grit, and mix it with oil. This can then be put on a wiper which will snugly fit the bore, and the barrel may then be put in the lathe and rotated at a high rate of speed with the wiper in the bore, and during the rotation the wiper is drawn in and out. This operation should be continued for an hour at least, frequently withdrawing it to add more of the polishing grit."
"What is the best grit to use?"
"If we can find a sample of the adamantine spar, in sufficient quantities, it would be the best substance."
"What kind of material is that?"
"It is a substance known as corundum."
"Is that the same as emery?"