life, but that no kind of life can exist
without it. Finally, Priestley's great discovery proved to be of
direct practical utility, since the successful pursuit of innumerable
trades and manufactures, with the profitable separation of metals from
their ores, stands in close connection with the facts which his
experiments with oxygen made known.

As intellectual light spread, so also did material light. In London,
up to near the close of the reign of George III, only a few feeble oil
lamps were in use. Many miles of streets were dark and dangerous, and
highway robberies were frequent. At length (1815) a company was
formed to light the city with gas. After much opposition from those
who were in the whale-oil interest the enterprise succeeded. The new
light, as Miss Martineau said, did more to prevent crime than all the
Government had accomplished since the days of Alfred. It changed,
too, the whole aspect of the English capital, though it was only the
forerunner of the electric light, which has since changed it even
more.

The sight of the great city now, when viewed at night from Highgate
archway on the north, or looking down the Thames from Westminster
Bridge, is something never to be forgotten. It gives one a realizing
sense of the immensity of "this province covered with houses," which
cannot be got so well in any other way. It bring to mind, too, those
lines expressive of the contrasts of wealth and poverty, success and
failure, inevitable in such a place:

"O gleaming lamps of London, that gem the city's crown,
What fortunes lie within you, O lights of London town!
. . . . . . . . . . .
O cruel lamps of London, if tears your light could drown,
Your victims' eyes would weep them, O lights of London town."[1]

[1] From the play, "The Lights of London."

The same year in which gas was introduced, Sir Humphry Davy invented
the miner's safety lamp. Without seeking a patent, he generously gave
his invention to the world, finding his reward in the knowledge that
it would be the means of saving thousands of lives wherever men are
called to work underground.

565. Steam Navigation, 1807, 1819, 1840.

Since Watt had demonstrated the value of steam for driving machinery
(S563), a number of inventors had been experimenting with the new
power, in the hope that they might apply it to propelling vessels. In
1807 Robert Fulton, an American