The Bunsen burner, to which reference has been made already, burns with a non-luminous flame, often called a "blue flame," and, burning the gas more completely, no carbon particles remain to be rendered incandescent. Dr. Welsbach conceived the idea of using such a flame to heat to incandescence a cage or mantle comprised of mineral matter.

Sectional view, showing the simple construction of the

"Bunsen burner" as applied to gas

We have seen how the idea has developed in incandescent gas lighting, and why it has proved, light for light, a more economical means of illumination than the old batswing burner.

The cost of mantles, if not frequently destroyed by careless treatment, is negligible, and does not materially affect the economy of the system.

Improvements, unnoted by the public, have been made in the structure and composition of the mantle, in part to render the light whiter and in part to reduce the liability to breakage.

The advantage of gas over oil is in the smaller amount of trouble involved in the management, and, no doubt, this warrants its preference wherever a gas-lighting system is available. The relative cost is shown in the table given above.

The householder who instals incandescent gas lighting should remember that the economy of this system over the old yellow-flame gas lighting is not only represented by the higher candle-power of the burner, but also by a very material reduction in the amount of gas burnt, the cost per 1,000 candles per hour being 2 1/2d., against is. for the batswing burner, with gas at 3s. per cubic foot. Hence it is false economy to fit incandescent burners in the living-rooms and to light the kitchen quarters, bedrooms, etc., with the ordinary batswing burners.

At the same-time, with a view to economy of mantles and chimneys, it is well that some responsible person should see to renewals, as servants are not always to be trusted to do this without mishap.

Burners that are in use intermittently should be fitted with bypass burners, so that they may be turned on without the necessity for re-lighting, because mantles are apt to be broken by matches dropped upon them, or by the mild explosion that results from careless lighting.

The choice of inverted or upright mantles is principally one of taste, and hardly affects the question of economy. The inverted burner casts no shadows, and may be placed nearer to the ceiling, but, light for light, the cost for gas is practically the same.

Electricity

The old carbon filament incandescent lamp laid the foundation of our modern systems of domestic electric lighting. Its advantages over the gas flame were so considerable in certain directions that it has easily usurped first place. Yet in the one question of cost it has never been able to show an advantage over, or even a near approach to, the economy of gas. In spite of this disability, however, electric lighting on the incandescent system is generally considered worth while, on account of its hygienic advantages, its cleanliness, and the ease with which it is turned on and extinguished. Thus, when considering the relative economy of electric light and gas, we must take these points into account.

A good type of inverted incan-descent burner and shade. Such burners cast no shadows, and may be placed near a ceiling, if desired

Another form of inverted incandescent burner of good and useful design

Blanchard

"The Tantalum," a metal filament lamp that gives a good light with a low consumption of electric current

The first one, hygiene, is not to be measured in £ s. d., but it should carry some weight, for, after all, a pure atmosphere in our living-rooms is worth some outlay to ensure.

In the matter of cleanliness there may well be a very material saving in decorations by adopting electric light. Lastly, the eas with which the light is started and extinguished is a saving of trouble, and conduces materially to economy, for the light may be extinguished by a touch of the switch whenever it is not wanted, whereas a gas light will generally be left burning to save the trouble of re-lighting it.

At current rates, electric lighting is a luxury. Already, however, there are signs of hopeful improvements in the direction of economy, if not in reduced cost of current, at least in lamps that give the same light with a lower consumption of current. These are the recently introduced metal filament lamps, of which several makes are now on the market. Taking the well-known "Tantalum " lamp as the example to compare with the carbon filament lamp, it will be found that the same candle-power is obtained for about half the consumption of current.

Added to this there is a larger effective life compared with the carbon lamp, because the Tantalum does not fall off in efficiency as rapidly as the carbon lamp. Thus it is claimed that the metal filament lamp shows a saving of 60 per cent. over the carbon lamp after both have burnt for 600 hours.

Another improvement is the new "Tungsten" lamp, which is stated to consume 1 watt per candle-power, as compared with 3 1/2 for the carbon lamp, and hence has been put out under the name " One watt " lamp. Another point in favour of these lamps is the great strength of their filaments, which reduces the chance of breakage. To be continued.