A unit of luminous intensity legalized by the 1860 Metropolitan Gas Act¹ (the British Parliamentary candle). The British standard candle was the luminous intensity of an actual standardized candle, made from spermaceti with a melting point of 112°–115°F, with a bit of beeswax added to control brittleness. The length was 10 inches, the bottom diameter 0.9 inches and the top diameter 0.8 inches. It burned at a rate of 120 ± 6 grains per hour. (Some describe the candle as ⅞ inch in diameter, weighing ¹⁄₆th of a troy pound.)
1. 23 & 24 Victoria, chapter 125, paragraph 25 (1860).
The English photometric candle is the spermaceti candle, 6 to the pound, burning 2 grains of material per minute, or 120 grains (7.776 grams) per hour. Schwendler says 8.26 grams. The dimensions of the candle are: length, 252 mm.; diameter at top, 20 mm.; at bottom, 22.5 mm.; mean weight, 75.7 grams.
When the real consumption of the candle differs from this figure, and is between 114 and 126 grains per hour, we assume that the illuminating power is proportional to the consumption, and correction is made by means of a simple proportion. The wick is made of three strands of cotton, each containing from 18 to 21 threads, according to the brand.
The height of flame adopted is 45 mm. The composition and purity of spermaceti are liable to considerable variation, according to the source and method of refining.
Thus Heisch and Hartley mention the fact, with the proof, that spermaceti candles now give more light for the same weight of matter burned than formerly. This is due to small improvements in the wicks or to progress in the treatment of spermaceti.
A Treatise on Industrial Photometry with Special Attention to Electric Lighting.
Authorized translation from the French by George W. Patterson, Jr., and Merib Rowley Patterson.
New York: Van Nostrand Co, 1894.
Pages 122. The first French edition, Traité de Photométrie Industrielle Spécialement Appliquée à L’Éclairage Électrique, was published in 1892.
From 1898, the Metropolitan Gas Referees Notification (London) candle is ¹⁄₁₀th of the output of a certain type of Harcourt pentane lamp, namely the one equipped with Sugg's Standard London Argand burner, No. 1, with a Methven screen.
Earlier in the 19ᵗʰ century, the quality of grades of coal gas was already being described in “candles”, but we do not know how it was defined.
Young's Paraffin Oil.—When burned in Young's lamps, two gallons yield a light equal to 1,000 cubic feet of 10-candle gas.
Notes and Queries, series 7, vol 2 (December 11, 1886). Advertisement inside back cover.
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