That discover “laid the foundation of modern chemical science.”  It enlarged our knowledge of the composition of the atmosphere, of the solid crust of the earth, and of water.  Furthermore, it revealed the interesting fact that oxygen not only enters into the structure of all forms of animal and vegetable 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, built the first successful steamboat, and made the voyage from New York to Albany in it.  Shortly afterwards his vessel began to make regular trips on the Hudson.  A number of years later a similar boat began to carry