It is perhaps necessary to refer to the more extended use of candles for lighting in some few houses in which lamps are disliked on aesthetic, or, in some cases, ostensibly on hygienic grounds. Candle lighting, speaking broadly, is either very inadequate so far as ordinary living-rooms are concerned, or, if adequate, is very costly. Tests specially carried out by one of the authors to determine some of the figures required in the ensuing table show that ordinary paraffin or "wax" candles usually emit about 20 per cent. more light than that given by the standard spermaceti candle, whose luminosity is the unit by which the intensity of other lights is reckoned in Great Britain; and also that the light so emitted by domestic candles is practically unaffected by the sizes--"sixes," "eights," or "twelves"--burnt. In the sizes examined the light evolved has varied between 1.145 and 1.298 "candles," perhaps tending to increase slightly with the diameter of the candle tested. Hence, to obtain illumination in a room equal on the average to that afforded by 100 standard candles, or some other light or lights aggregating 100 candle- power, would require the use of only 80 to 85 ordinary paraffin, ozokerite, or wax candles. But actually the essential objects in a room could be equally well illuminated by, say, 30 candles well distributed, as by two or three incandescent gas-burners, or four or five large oil- lamps. Lights of high intensity, such as powerful gas-burners or oil- lamps, must give a higher degree of illumination in their immediate vicinity than is really necessary, if they are to illuminate adequately the more distant objects. The dissemination and diffusion of their light can be greatly aided by suitable colouring of ceilings, walls and drapings; but unless the illumination by means of lights of relatively high intensity is made almost wholly indirect, candles or other lights of low intensity, such as small electric glow-lamps, can, by proper distribution, be made to give more uniform or more suitably apportioned illumination. In this respect candles have an economical and, in some measure, a material advantage over acetylene also. (But when the method of lighting is by flames--candle or other--the multiplication of the number of units which is involved when they are of low intensity, seriously increases the risk of fire through accidental contact of inflammable material with any one of the flames. This risk is much greater with naked flames, such as candles, than with, say, inverted incandescent gas flames, which are to all intents and purposes fully protected by a closed glass globe.) Hence, in the tabular statement which follows of the comparative cost, &c., of different illuminants, it will be assumed that 30 good candles would in practice be equally efficient in regard to the illumination of a room as large oil-lamps, acetylene flames, or incandescent gas-burners aggregating 100 candle-power.