. The Civil engineer and architect's journal, scientific and railway gazette. Architecture; Civil engineering; Science. 1839.] THE CIVIL ENGINEER AND ARCHITECTS JOURNAL. .329 commonly taken us the standard. I do not think it entitled to this pre-eminence : for it may be made to emit very different qnantities of light, according to differences in the natnre and supply of the oil, as well as variations in the form and position of the chimney. Besides, such lamps are too rare in this country to be selected as standards of illumination. After comparing lights of many kinds, I find every reason to
. The Civil engineer and architect's journal, scientific and railway gazette. Architecture; Civil engineering; Science. 1839.] THE CIVIL ENGINEER AND ARCHITECTS JOURNAL. .329 commonly taken us the standard. I do not think it entitled to this pre-eminence : for it may be made to emit very different qnantities of light, according to differences in the natnre and supply of the oil, as well as variations in the form and position of the chimney. Besides, such lamps are too rare in this country to be selected as standards of illumination. After comparing lights of many kinds, I find every reason to con- clude, tliat a large wax candle of three to the pound, either long or short, that is, either 12 or 15 inches in length, as manufactured by one of the great wax-chandlers of London, and furnished with a wick con- taining 27 or 2S threads of the best Turkey cotton, is capable of fur- nishing a most uniform, or nearly invariable standard of illumination. It affords one-tenth of the light emitted by one of (he Argand lamps of the Trinity House, and one-eleventh of the light of my mechanical lamp, when each lamp is made to burn with its maxiuunn Hauie, short of smoking. The great obstacle to the combustion of lamps, lies in the viscidity, and consequent sluggish supply, of oil, to the wicks; an obstacle nearly insuperable with lamps of the common construction during the winter months. The relative viscidity, or relative fluency of different liquids at the same temperature, and of the same liquid at different tempera- tures, has not, I believe, been hitherto made the subject of accurate researches. I was, therefore, induced to make the following experi- ments with this view. Into a hemispherical cup of platinum, resting on the ring of a che- mical stand, I introduced 2000 water-grain measures of the liquid whose viscidity was to be measured, and ran it off through a glass syphon, i of an inch in the bore, having the outer leg 3i inches, and tlie inner leg 3 inches long. The time
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