129 feet in length; 24 feet 6 inches beam; and 15 feet in depth; measured tonnage, 360 tons; nominal power, 100 horses.

TONS.

Tons, 494.

With this displacement, she draws 12 feet 6 inches aft, 11 feet 4 inches forward, in sea-water, and the area of her midship section, immersed, is about 213 feet.

Her hull weighs .........................

250

Her engines ..............................

104

Provisions, stores, masts, anchors, etc. .....................

30

Coals .........................................

110

Her cylinders are 39 inches in diameter, with a 3 feet 6 inch stroke. Her wheels are 17 feet in diameter, and 5 feet 2 inches wide.

When the vessel is deep, her wheels revolve.........

from 14 to 20 times per minute in heavy weather, and from 20 to 25 times in light weather.

When the vessel is light, their speed increases . . . . . . . . . . . . . . . . . .

from 16 to 22 times per minute in heavy weather, and from 26 1/5 to 28 per minute in light weather.

The Firefly

156 feet in length; 28 feet 2 inches beam; depth, 17 feet; measured tonnage, 560; nominal power, 140 horses.

TONS.

Tons,

715.

With this displacement, she draws 12 feet aft, and 11 feet 4 inches forward, in sea-water, and the area of her midship section, immersed, is about 270 feet.

Her hull weighs .......................

330

Her engines.....

150

Provisions, stores, masts, anchors, etc. .....................

35

Coals .......................................

200

Her cylinders are 44 inches in diameter, with a 4 feet 6 inch stroke. Her wheels are 18 feet in diameter, and 9 feet 2 inches wide.

When the vessel is deep, her wheels

from 17 to 19 times per minute in smooth water, and from 6 to 12 per minute in heavy weather.

When the vessel is light, their speed

' from 20 to 21 revolutions per minute in fine weather, and from 8 to 14 in heavy weather.

The displacement certainly offers a better standard than the measured tonnage for estimating the power required in steam vessels; but we think the area of the immersed transverse section is the best basis of calculation; for, upon this the resistance chiefly depends. Thus, a steam-boat which has been lengthened generally sails faster with the same engines than before; because, although her measured tonnage is thereby increased, yet, from drawing less water, the area of the immersed transverse section is diminished.

In the three examples just given, the sectional area is to the horse power as follows:

Flamer......................

1.9

feet area to 1 horse-power.

Columbia ........

213

"

"

"

Firefly......................

1.6

"

"

"

A fair proportion seems to be from 1 1/2 foot to 2 feet section per horse-power, according to the nature of the service for which the vessel is intended.