Best Lantern with Russian Iron Body and Stocks' Lamp.
The selection of illuminant is the thing that puzzles the prospective lanternist more than anything else, and, undoubtedly, much of his own pleasure depends on its power and efficiency. Still, it must not be imagined that the most powerful light is necessary, particularly when using a lantern at home, providing it is recognised that the size of the picture on the screen should not be greater than can be effectually illuminated.
The illuminants in general use, with their approximate candle powers, are as follows • THE LIGHT.
50 to 100
Four-wick Paraffin Oil Lamp......
Stocks' Paraffin Oil Lamp ......
Three-burner Acetylene Jets ......
Four-burner do. ......
Luna Spirit Lamp......................
• • 300
Kama Electric Lamp, with 3 Nernst filaments,
" " "
Blow Through Jets
. . .. 500
High-Power Ejector Jets
Arc Lamp from usual house supply
Arc Lamps with main supply
1000 to 3000
Or more according to current consumed.
These candle powers are only very approximate and are makers' estimates, but serve to give some relation between the powers of the various lights.
For those who have gas Or electricity laid on in their houses, and who want something that will be the least trouble, some light which may be used from the house supply will appeal. For gas users, who are not requiring a very powerful light, an incandescent burner will be favoured. The most powerful form for lantern use is what is known as the " Block Light," but this is only suitable for a lantern with a good-sized body, because of the distance from the bottom of the burner to the centre of the light. Such a light is admirable for a picture not exceeding 3 or 4 feet in diameter.
OIL AND SPIRIT LAMPS.
Oil Lamps were formerly the rule in country districts where gas and electricity were unknown, but these have been almost superseded by incandescent spirit lamps. With these lamps, methylated spirit is heated and vaporized, and the vapour mixed with air burns from a bunsen burner and makes a mantle incandescent. The best forms force the mixture " Luna " Spirit Lamp." of vapour and air, under pressure, through the burner. This pressure is obtained, in the case of the Regent Lamp, by means of a small pump at the rear of the spirit reservoir, the piston of which is raised and lowered once or twice every few minutes, but in the Luna Lamp it is automatic, due to the vaporization of the spirit by means of heat. The reservoir has a safety valve at the back to relieve the pressure, should it prove greater than the mantle is likely to stand.
Electricity is now becoming so general that, for those who have it at command, the Kama Electric Lamp is recommended. This lamp can be attached to any ordinary electric light fitting and gives a very powerful light. Of course, it is not without some drawbacks, the principal being the breakage which occurs with the filaments without apparent cause, and the renewals of the filaments cost 3s. each. Sometimes the filaments last for months and at other times may fail in a few days. Yet the light is so good and the consumption of current so small that its advantages outweigh its disadvantages. The Kama Lamp for Lantern use fitted with three filaments in the form of a star costs £2 10s., and the voltage of the house supply must be mentioned when ordering. In my own practice, I frequently use a broken filament for a longer time than when it is whole, by supporting one broken end in contact with the other broken end, and, indeed, such a filament gives more light than one that is whole, because it is reduced in length.
Kama No. 3 Burner.
Small Arc Lamps suitable for the supply from the ordinary house fittings are preferred by some workers, although they need greater attention, but have the advantage of giving a sharper picture on the screen, owing to the smaller points of light.
The ordinary carbon or metallic filament lamps used for house lighting are quite unsuitable for lantern use.
Acetylene, if a little more trouble than house gas or electric light, has many points to recommend it, and is very serviceable for those wishing for a cheap light that is sufficiently powerful to be used in a village school-room. The quality of the light is also of such a character that it may be used with advantage to show colour plates such as autochromes, but of course these, on account of their density must, with such a light, not be enlarged to more than about 18 inches square. The apparatus used for the production of the gas is inexpensive and simple, and is known as an acetylene generator. Apart from the generator, the only requisites are calcium carbide and water. Calcium carbide is obtained by subjecting a mixture of lime and coal to get heat, and has the peculiar property of giving off the acetylene gas when water comes into contact with it.