PARAFFIN-OIL LAMPS, INCANDESCENT GAS AND SPIRIT BURNERS
There are several varieties of oil lamps on the market, but in practically every case they take the same general form, a metal reservoir sliding in grooves in the lantern body and holding approximately a pint of oil with (usually) four wicks nearly parallel, but slightly converging from rear to front, these enclosed in a flame chamber of Russian iron, with loose well-annealed ends of sheet glass and an adjustable reflector at the back, or sometimes the reflector itself forms the rear end of the flame chamber. The chimney must be tall and is now usually made adjustable, though I have never been able to trace any real advantage from this complication
(Fig. 1). The whole secret of obtaining the best results from these lamps may be summed up—good oil and perfect cleanliness; and it is wonderful what can be done when these points are properly attended to.
Care should be taken in trimming the wicks to see that no charred parts fall down between the wick holders, but it makes little difference whether the trimming is done with scissors or by rubbing with the finger. Special lamp scissors are sold by all makers with a large flat on one side to catch the portions cut off.
These lamps should be well rubbed over the last thing before use, as paraffin-oil is apt to 'creep,' and the operator does not want to be told that his apparatus is suggestive of a fried fish shop. In working with these lamps it is difficult to avoid a dark streak down the centre of the sheet, representing the space between the two centre wicks; to a certain extent this can be obviated by adjusting the reflector, and in any case is not very obvious when the slide is in place. Lamps constructed with either three or five wicks are better in this respect, but the former are usually considered to be too poor in illuminating power, and the latter are apt to crack the sheet-glass ends by excessive heat.
Incandescent Gas.—Incandescent gas burners do not need much description, as they are practically similar to those in general use for house lighting. They may be either of the erect or inverted forms, the latter being preferable owing to the light being more concentrated, and a reflector is provided to increase the illumination (Fig. 2).
These reflectors should be spherical and so adjusted that the radiant is in the centre of curvature, thus ensuring that the light from the reflector passes again through the original source. If this point is not attended to, we shall be dealing with essentially two sources of light instead of one, to the detriment of the definition.
The same remark applies to every lantern illuminant
which is supplemented by a reflector, and it is extraordinary how often it is neglected by the manufacturer. Of course the opacity of the illuminant destroys much of the efficiency of the reflector, and hence in the case of incandescent gas mantles there is not much real gain in making use of them, but with these comparatively weak illuminants every fraction tells, and the reflector does not add much to the cost.