r is the fuel. Incidentally, these lamps also supply the only
artificial heat for their huts and igloos. The heat from these feeble
light-sources and from their bodies keeps these natives of the arctics
warm within the icy walls of their abodes.

Very beautiful oil-lamps of brass, bronze, and pewter evolved in such
countries as Egypt. Many of these were designed for and used in
religious ceremonies. The oil-lamps of China, Scotland, and other
countries in later centuries were improved by the addition of a pan
beneath the oil-receptacle, to catch drippings from the wick or oil
which might run over during the filling. The Chinese lamps were
sometimes made of bamboo, but the Scottish lamps were made of metal. A
flat metal lamp, called a crusie, was one of the chief products of
blacksmiths and was common in Scotland until the middle of the
nineteenth century. This type of lamp was used by many nations and has
been found in the catacombs of Rome. The crusie was usually suspended by
an iron hook and the flow of oil to the wick could be regulated by
tilting. The wick in the Scottish lamps consisted of the pith of rushes,
cloth, or twisted threads. These early oil-lamps were almost always
shallow vessels into which a short wick was dipped, and it was not until
the latter part of the eighteenth century that other forms came into
general use. The change in form was due chiefly to the introduction of
scientific knowledge when mineral oil was introduced. As early as 1781
the burning of naptha obtained by distilling coal at low temperatures
was first discussed, but no general applications were made until a later
period. This was the beginning of many marked improvements in oil-lamps,
and was in reality the birth of the modern science of light-production.

[Illustration: A TYPICAL METAL MULTIPLE-WICK OPEN-FLAME OIL-LAMP]

[Illustration: A GROUP OF OIL-LAMPS OF TWO CENTURIES AGO]

As the activities of man became more complex he met from his growing
store of knowledge the increasing requirements of lighting. In
consequence, many ingenious devices for lighting were evolved. For
example, in England in the seventeenth century man was already burrowing
into the earth for coal and of course encountered coal-gases. These
inflammable gases were first known for the direful effects which they so
often produced rather than for their useful qualities. Although they
were known to miners long before they received scientific attention, the
earlie