The Wonder Island Boys | Page 9

12 parts tin and 88 of copper; Egyptian, 22 tin, 78 copper; Chinese, 20 tin, 80 copper; Roman, 15 tin, 85 copper; and in many specimens lead and zinc were also used. Tin has a capacity to harden almost any metal."
"What is the best metal to harden steel?"
"Manganese, of which you will remember we have some samples; it is the most serviceable, as we have neither nickel nor chromium."
"What amount of that metal should we use to get the best results?"
"About 14 per cent. of manganese has been found the best for such purposes as would be required in gun barrels. There is a curious thing which has been discovered in uniting manganese with steel. It becomes fairly tough if 1 per cent. is used with the steel; if the quantity added is between 1-1/4 and 3-1/2 the strength and ductility decrease; but above that, up to 5 per cent., the steel becomes brittle; above 6-1/2 per cent. it again returns to ductility and toughness and its maximum strength is found at 14 per cent."
During the evenings all took a hand at cutting out the stocks for the guns, and the plans upon which they were constructed will be fully explained and illustrated in the order of the work done.
Meanwhile it must not be supposed that work on the new boat had ceased. Harry's plan, when fully worked out, provided for one twenty feet long and six and a half feet wide amidships.
The drawing (Fig. 2) shows the construction of the hull. As they had no means for doing any fancy bending of the boards, the bottom was made flat, and the sides sloping. The bottom and the sides were made in the following manner: Two stringers (A, A) were first constructed, which were made up of thin pieces nailed together, so they could be bent in the proper shape for the bottom boards, which were laid crosswise and nailed to these stringers.
[Illustration: Fig 2. TOP VIEW OF BOAT]
[Illustration: Fig 3. SIDE VIEW]
For the upper edges of the sides, called the gunwale (B, B), similar stringers were provided, but they extended farther fore and aft, and amidships were fully six and a half feet apart, whereas the lower stringers amidships were four and a half feet apart. This arrangement, therefore, provided for sloping sides, and the side pieces ran up and down on the inner course. It will be understood that the sides and bottom thus formed were to be overlaid with thin boards running fore and aft, as in Fig. 2, as they had no means for matching the boards and thus putting them together tightly.
The sides were two and a half feet high. Six and a half feet from the forward end was a cross beam (C), into which the mast was to be stepped. At the stern the bottom was sloping upwardly at an angle and brackets (D) were extended back and joined at their rear ends, to which the lower end of the rudder post was attached.
Amidships a keel (E) was formed, projecting down from the bottom, this keel being, at its widest part, two feet, and tapering down to merge with the bottom, fore and aft. The cross section (Fig. 4) shows how well he had formed the vessel, proportionally.
[Illustration: Fig. 4. Cross Section.]
In addition to the cross seats, similar arrangements for comfort were made along the sides, and beneath the side seats were spaces in which their supplies were to be placed. The space forward of the mast was entirely closed over with a roof which sloped in both directions, and here provision was made for two berths. This would also afford them protection and serve as a means to keep out the water and insure at least one dry spot for their comfort.
As usual, George had some inquiries to make about the boat. "It has always been a matter of wonder why all boats are made with the big bulging part nearest the forward end?"
The Professor's eyes twinkled. "Probably there are a great many others who have had such thoughts. There is really no reason for it. It is not known how the custom originated, except that in sailing vessels the claim is that the ship can be maneuvered more easily by such construction."
"In what way does it make it easier to handle?"
"When a ship is driven forward by the wind, all the force exerted on the sails is transferred to the forward part of the ship, hence if made narrow at its forward end it would be driven down into the water, and the hull would, therefore, be submerged more at the forward than at the rear end. Furthermore, by having a tapering rear end, the rudder has a better opportunity of veering the ship around and you can see that the