protected by a closed glass globe.) Hence, in the tabular statement which
follows of the comparative cost, &c., of different illuminants, it will
be assumed that 30 good candles would in practice be equally efficient in
regard to the illumination of a room as large oil-lamps, acetylene
flames, or incandescent gas-burners aggregating 100 candle-power.

For the same reason it will be assumed that electric glow-lamps of low
intensity (nominally of 8 candle-power or less), aggregating 70-80
candle-power, will practically serve, if suitably distributed, equally as
well as 100 candle-power obtained from more powerful sources of light.
Electric glow-lamps of a nominal intensity of 16 candles or thereabouts,
and good flat-flame gas-burners, aggregating 90-95 candle-power, will
similarly be taken as equivalent, if suitably distributed, to 100 candle-
power from more powerful sources of light. Of the latter it will be
assumed that each source has an intensity between 20 and 30 candle-power,
such as is afforded by a large oil-lamp, a No. 1 Welsbach-Kern upturned,
or a "Bijou" inverted incandescent gas-burner, or a 0.70-cubic-foot-per-
hour acetylene burner. Either of these sources of light, when used in
sufficient numbers, so that with proper distribution they light a room
adequately, will be taken in the tabular statement which follows as
affording, per candle-power evolved, the standard illuminating effect
required in that room. The same illuminating effect will be regarded as
attainable by means of candles aggregating only 35 per cent., or small
electric glow-lamps aggregating 77 per cent., or large electric glow-
lamps and flat-flame gas-burners aggregating 90 to 95 per cent. of this
candle-power; while if sources of light of higher intensity are used,
such as Osram or Tantalum electric lamps, or the larger incandescent gas-
burners (the Welsbach "C" or "York," or the Nos. 3 or 4 Welsbach-Kern
upturned, or the No. 1 or larger size inverted burners) or incandescent
acetylene burners, it will be assumed that their aggregate candle-power