Drummond's apparatus was so constructed that the lamp fed itself automatically with spirit and with oxygen, supplying itself with balls of lime as they were gradually consumed, and was provided with a parabolic silvered copper mirror.
With this apparatus the light produced by a ball of lime 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