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statutory power should be obtained for that mode of testing,
so that the companies may be liable to forfeitures for gas
which the portable photometer shews to be defective in lighting
power.
Standard of Light.— The Metropolitan Board, also in
1884, suggested the expediency of an alteration in the standard
of light prescribed by the statutes. It is required that the
illuminating power of the gas shall, when consumed at the
rate of five cubic feet an hour, by means of a standard argand
gas burner, be equal in intensity to the light given by 16
sperm candles of 6 to the pound, each burning at the rate
of 120 grains per hour. A Committee, appointed by the
Board of Trade, reported adversely to the continuance of the
use of the sperm candle as a standard, it having been proved
that, in spite of precautions taken to secure uniformity in
the manufacture of the candles, there remained considerable
variation in the lighting power. In the Report of the Board
for 1887, the subject was again dealt with, and we were
informed that, in the interval, a long series of careful and
complete experiments had been made by the Officers of
the Board, under the Board's authority, with the result that
the Pentane air-gas standard, as devised by Mr. A. Vernon
Harcourt, one of the gas referees, appeared to possess, in a
higher degree than any other, the merits of simplicity,
accuracy and reliability. The County Council, through its
Sanitary and Special Purposes Committee, took up the
subject, having addressed a communication to the Board of
Trade (in July, 1889), with a view to steps being taken
for (1) providing a trustworthy standard of light; (2) prescribing
a standard photometer with which all official photometers
should be compared, and (3), giving legal force to
tests made with a portable photometer; the reasons for
which are fully set out in the Committee's communication.
During 1891 the subject continued to receive the attention
of the Committee, and formed the subject of several reports.