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 earliest account of them in the Transactions of the Royal Society was presented in the year 1667. A description of early gas-lighting has been reserved for a later chapter, but the foregoing is noted at this point to introduce a novel early method of lighting in coal-mines where inflammable gases were encountered. In discussing this coal-gas another early writer stated that "it will not take fire except by flame" and that "sparks do not affect it." One of the early solutions of the problem of artificial lighting under such conditions is summarized as follows: