Professor Phin, of the Manufacturer and Builder, has kindly given us some late information on this important topic, which will be found valuable.
In choosing the source of our light, the great points to be considered are, first, the influence on the eyes; and secondly, economy. It is poor economy to use a bad light. Modern houses in cities, and even in large villages, are furnished with gas; where gas is not used, sperm-oil, kerosene or coaloil, and candles are employed. Gas is the cheapest, (or ought to be;) and if properly used, is as good as any. Good sperm-oil burned in an Argand lamp - that is, a lamp with a circular wick, like the astral lamp and others - is perhaps the best; but it is expensive and attended with many inconveniences. Good kerosene-oil gives a light which leaves little to be desired. Candles are used only on rare occasions though many families prefer to manufacture into candles the waste grease that accumulates in the household. The economy of any source of light will depend so muck upon local circumstances that no absolute directions can be given.
The effect produced by light on the eyes depends upon the following points: First, Steadiness. Nothing is more injurious to the eyes than a nickering, unsteady flame. Hence, all flames used for light-giving purposes ought to be surrounded with glass chimneys or small shades. No naked flame can ever be steady. Second, Color. This depends greatly upon the temperature of the flame. A hot flame gives a bright, white light; a flame which has not a high temperature gives a dull, yellow light, which is very injurious to the eyes. In the naked gas-jet a large portion of the flame burns at a low temperature, and the same is the case with the flame of the kerosene lamp when the height of the chimney is not properly proportioned to the amount of oil consumed; a high wick needs a high chimney. In the case of a well-trimmed Argand oil-lamp, or an Argand burner for gas, the flame is in general most intensely hot, and the light is of a clear white character.
The third point which demands attention is the amount of heat transmitted from the flame to the eyes. It often happens that people, in order to economize light, bring the lamp quite close to the face. This is a very bad habit. The heat is more injurious than the light. Better burn a larger flame, and keep it at a greater distance.
It is also well that various-sized lamps should be provided to serve the varying necessities of the household in regard to quantity of light. One of the very best forms of lamp is that known as the "student's reading-lamp," which is, in the burner, an Argand. Provide small lamps with handles for carrying about, and broad-bottomed lamps for the kitchen, as these are not easily upset. Hand and kitchen lamps are best made of metal, unless they are to be used by very careful persons.
Sperm-oil, lard, tallow, etc., have been superseded to such an extent by kerosene that it is scarcely worth while to give any special directions in regard to them. In the choice of kerosene, attention should be paid to two points: its safety, and its light-giving qualities. Kerosene is not a simple fluid, like water; but is a mixture of several liquids, all of which boil at different temperatures. Good kerosene-oil should be purified from all that portion which boils or evaporates at a low temperature; for it is the production of this vapor, and its mixture with atmospheric air, that gives rise to those terrible explosions which sometimes occur when a light is brought near a can of poor oil. To test the oil in this respect, pour a little into an iron spoon, and heat it over a lamp until it is moderately warm to the touch. If the oil produces vapor which can be set on fire by means of a flame held a short distance above the surface of the liquid, it is bad. Good oil poured into a tea-cup or on the floor does not easily take fire when a light is brought in contact with it. Poor oil will instantly ignite under the same circumstances, and hence the breaking of a lamp filled with poor oil is always attended by great peril of a conflagration. Not only the safety but also the light-giving qualities of kerosene are greatly enhanced by the removal of these volatile and dangerous oils. Hence, while good kerosene should be clear in color, and free from all matters which can gum up the wick and thus interfere with free circulation and combustion, it should also be perfectly safe. It ought to be kept in a cool, dark place, and carefully excluded from the air.
The care of lamps requires so much attention and discretion, that many ladies choose to do this work themselves, rather than trust it with domestics. To do it properly, provide the following things: an old waiter to hold all the articles used; a lamp-filler, with a spout, small at the end, and turned up to prevent oil from dripping; proper wicks, and a basket or box to hold them; a lamp-trimmer made for the purpose, or a pair of sharp scissors; a small soap-cup and soap; some washing soda in a broad-mouthed bottle; and several soft cloths to wash the articles and towels to wipe them. If every thing, after being used, is cleansed from oil and then kept neatly, it will not be so unpleasant a task as it usually is to take care of lamps.
The inside of lamps and oil-cans should be cleansed with soda dissolved in water. Be careful to drain them well, and not to let any gilding or bronze be injured by the soda coming in contact with it. Put one table-spoonful of soda to one quart of water. Take the lamp to pieces and clean it as often as necessary. Wipe the chimney at least once a day, and wash it whenever mere wiping fails to cleanse it. Some persons, owing to the dirty state of their chimneys, lose half the light which is produced. Keep dry fingers in trimming lamps. Renew the wicks before they get too short. They should never be allowed to burn shorter than an inch and a half.
In regard to shades, which are always well to use on lamps or gas, those made of glass or porcelain are now so cheap that we can recommend them as the best without any reservation. Plain shades, making the light soft and even, do not injure the eyes. Lamps should be lighted with a strip of folded or rolled paper, of which a quantity should be kept on the mantel-piece. Weak eyes should always be especially shaded from the lights. Small screens, made for the purpose, should be kept at hand. A person with weak eyes can use them safely much longer when they are protected from the glare of the light. Fill the entry-lamp every day, and cleanse and fill night-lanterns twice a week, if used often. A good night-lamp is made with a small one-wicked lamp and a roll of tin to set over it. Have some holes made in the bottom of this cover, and it can then be used to heat articles. Very cheap floating tapers can be bought to burn in a tea-cup of oil through the night.