uel to the voyage, or the voyage to the
fuel. It is not necessary here to study very closely the economy of
fuel, as this is a question affecting the transport of freight alone.
When the mails are to be transported, economy of fuel is not the
object desired, but speed; and, consequently, we must submit to
extravagance of fuel. This large expenditure of coal is not necessary
in the case of freights, as they may be transported slowly, and,
consequently, cheaply. But one of the principal reasons for rapid
transport of the mails is that they may largely anticipate freights in
their time of arrival, and consequently control their movements.

I recently had an excellent opportunity of testing the large quantity
of fuel saved on a slight reduction of the speed, and give it as
illustrative of the law advanced. We were on the United States Mail
steamer "Fulton," Captain Wotton, and running at 13 miles per hour.
Some of the tubes became unfit for use in one of the boilers, and the
fires were extinguished and the steam and water drawn off from this
boiler, leaving the other one, of the same size, to propel the ship.
An intelligent gentleman who happened to know that we were using only
one boiler, and consequently, but half the power, remarked to me that
it was very strange that the ship was still going about eleven miles
per hour, without any sail. He said: "It is strange, sir; two boilers
of equal size drove us thirteen miles per hour; and here now but one
boiler drives us nearly eleven miles, or nearly as fast; when
common-sense teaches that the one boiler would drive us only six and a
half miles per hour. How is that?" I then explained to him very
clearly the natural law relative to power and speed, (_See Rule II.,
page 68_,) which he at once comprehended and admitted, but with the
remark: "Indeed, sir, I would have testified that she ought with one
boiler to have gone at only half the speed; or that going at six miles
with one boiler, she would go twelve with two."

As it will be interesting to the general reader to examine the details
of the increased consumption of fuel at increased rates of speed, I
present the following elaborate table recently prepared by Mr.
Atherton for his new edition of "Steamship Capability," according to
the formula above noticed, and the performance of the best type of
vessel in the Royal Navy, the steamer "Rattler." Mr. A. found a higher
efficiency in this vessel per horse power than any other in