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Knight's Mechanical Encyclopedia (ed. Knight) 2 0 Browse Search
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Knight's Mechanical Encyclopedia (ed. Knight), D. (search)
ime not larger than a boy's marble, at Londonderry, was visible at Belfast, a distance of nearly seventy miles, in a direct line. Subsequently, Colonel Colby made a lime-light signal visible from Antrim, in Ireland, to Ben Lomnd, in Scotland, a distance of ninetyfive miles in a straight line. It is stated that, intensified by a parabolic reflector, it has been observed at a distance of 112 miles. It is understood that the first application in practice was when it was required to see Leith Hill, in Surry, from Berkhampstead Tower, in Hertfordshire. The practical application was described in two papers published in the Philosophical Transactions of 1826 and 1831. The apparatus consists of a lamp which admits oxygen and hydrogen gas at the respective apertures o h. The gases come from separate holders, and do not mix till they reach the chamber c. Here they pass through several thicknesses of wire-gauze, which prevent explosion by the reflex action of the flame, and then issu