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VARIOUS LANTERN ILLUMINANTS. 27 a small disc will suffice, and a very powerful illumi- nant will not be necessary. On the other hand, if he aspires to giving public exhibitions or lantern shows, something in the nature of the lime-light or the electric arc-light will be required. Perhaps as the choice of an illuminant is so wide, it may be helpful to refer briefly to those in common use. These are constructed with three, and sometimes four, parallel wicks. If of good quality and properly trimmed they give a bright picture of from four to five- feet in diameter, and are very convenient and suitable for home use. The best oil should always be used, the surplus oil being poured out of the container after use, and the wicks dried, removed, and replaced. The latter must be kept carefully trimmed and straight. After lighting turn low until the lamp is thoroughly warmed, then raise by degrees. Wipe up- any oil accidentally spilt in filling the lamp. If these precautions are observed the lamp will burn well and will not smell. Never put camphor in the oil; it clogs the wicks, and increases the tendency to smoke. incandescent Where house gas is available, an in- Gas. candescent burner and mantel is a convenient and satisfactory illuminant for home ex- hibitions, but, like oil, is out of the question for pub- lic exhibitions. The burner is clamped on an ordinary lime-light tray, and must be adjusted so that the light is central with the optical system. A re- flector, though often used, is practically useless for this form of light. It gives a disc about equal in size to that thrown by an oil lamp, but the colour is whiter and more effective.