tors in lighting by candles because the whole "installation"
is consumed. This is an early example of which an authentic record is
available. At the present time a certain amount of light obtained for
$1.00 with efficient tungsten filament lamps, costs $2.00 if obtained
from kerosene flames and about $50.00 if obtained by burning candles.

In order to obtain the cost of an equivalent amount of light throughout
the past century a great many factors must be considered. Obviously, the
results obtained by various persons will differ owing to the unavoidable
factor of judgment; however, the following list of approximate values
will at least indicate the trend of the price of light throughout the
century or more of rapid developments in light-production. A fair
average of the retail values of fuels and of electrical energy and an
average luminous efficiency of the light-sources involved have been used
in making the computations. The figures apply particularly to this
country.

TABLE SHOWING THE APPROXIMATE TOTAL COST OF 1000 CANDLE-HOURS FOR
VARIOUS PERIODS

Per 1000
candle-hours
1800 to 1850, sperm-oil $2.40
tallow candle 5.00
1850 to 1865, kerosene 1.65
tallow candle 6.85
1865 to 1875, kerosene .75
tallow candle 6.25
gas, open-flame .90
1875 to 1885, kerosene .25
gas, open-flame .60
1885 to 1895, kerosene .15
gas, open-flame .40
1895 to 1915, gas mantle .07
carbon filament .38
metallized filament .28
tungsten filament (vacuum) .12
tungsten filament (gas-filled) .07

In these days the cost of living has claimed considerable attention and
it is interesting to compare that of lighting. In the following table
the price of food and of electric lighting are compared for twenty years
preceding the recent war. The great disturbance due to the war is
thereby eliminated from consideration, but it should be noted that since
1914 the price of food has greatly inc