s
previously occupied or filled with water. The oak block sinks to within
a short distance of the top because the oak is really just a trifle
lighter than water. If a pine block were placed in the water it would
sink only to the distance shown at _D_, since the weight of pine is less
than oak, or only 34.6 pounds per cubic foot. A pine block will, then,
displace only about 34.6 pounds of water, which leaves nearly half of
the block out of the water. Thus, it will be seen that for a given
volume (size) a cubic foot of wood will sink to a depth corresponding to
its weight. Different kinds of wood have different weights.

If a cubic foot of brass is placed in water, it will sink rapidly to the
bottom, because the brass is much heavier than water. How is it, then,
that an iron or concrete ship will float? If the cubic foot of brass is
rolled or flattened out in a sheet, and formed or pressed into the
shape of a boat hull, as shown in Fig. 2, it will float when placed upon
the surface of the water. Why is it that brass is caused to float in
this way, when it sank so rapidly in the form of a solid square?

[Illustration: FIG.2]

It will be remembered that the pine and oak block were caused to float
because they displaced a greater weight of water than their own weight.
This is just what causes the brass boat-hull to float. If the amount of
water actually displaced by the hull could be weighed, it would be found
that the weight of the water would be greater than the weight of the
hull. It will be understood that the space occupied by the brass
boat-hull is far greater than the space occupied by the block of brass
before it was rolled out and formed into a hull. What is true of brass
holds true of iron, steel, etc. A block of steel will not float, because
the water it displaces does not weigh nearly as much as the block. If
this block, however, were rolled out into a sheet and the sheet formed
into a hollow hull, the hull would float, because it would displace a
volume of water that would more than total the weight of the steel in
the hull.

In the case of the brass boat-hull, it would be found that a greater
portion of the hull would remain out of the water. The hull, then, could
be loaded until the top of it came within a safe distance from the
water. As the load is increased, the hull sinks deeper and deeper. The
capacity of big boats is reckoned in tons. If a boat had a carrying
capacity of ten tons it would sink to wha