of large spaces, where the steadiness and uniformity of the illumination
are of secondary importance. Under such conditions, it may be stated
parenthetically, the electric arc-light is much less costly than
acetylene lighting would be, but it is now in many places being
superseded by high-pressure gas or oil incandescent lights, which are
steady and generally more economical than the arc light.

The illuminant which acetylene is best fitted to supersede on the score
of convenience, cleanliness, and hygienic advantages is oil. By oil is
meant, in this connection, the ordinary burning petroleum, kerosene, or
paraffin oil, obtained by distilling and refining various natural oils
and shales, found in many countries, of which the United States
(principally Pennsylvania), Russia (the Caucasus chiefly), and Scotland
are practically the only ones which supply considerable quantities for
use in Great Britain. Attempts are often made to claim superiority for
particular grades of these oils, but it may be at once stated that so for
as actual yield of light is concerned, the same weight of any of the
commercial oils will give practically the same result. Hence in the
comparative statement of the cost of different methods of lighting, oil
will be taken at the cheapest rate at which it could ordinarily be
obtained, including delivery charges, at a country house, when bought by
the barrel. This rate at the present time is about ninepence per gallon.
A higher price may be paid for grades of mineral oil reputed to be safer
or to give a "brighter" or "clearer" light; but as the quantity of light
depends mainly upon the care and attention bestowed on the burner and
glass fittings of the lamp, and partly upon the employment of a suitable
wick, while the safety of each lamp depends at least as much upon the
design of that lamp, and the accuracy with which the wick fits the burner
tube, as upon the temperature at which the oil "flashes," the extra
expense involved in burning fancy-priced oils will not be considered