Some Account of' the Northern Light-Iiotises. 113 



and assistance of persons eminent in science, adopted parabolic 

 reflectors made of silvered copper; and these, from their supe- 

 rior effects, have ultimately been introduced into all the light- 

 houses of the United Kingdom. The reflectors which have for 

 many years been employed in the Northern Light-houses consist 

 of copper coated with silver, in the proportion of six ounces 

 of silver to one pound avoirdupois of copper, which are rolled 

 at the mills of Messrs Bolton and Watt, and, with much la- 

 bour and great nicety, by a process of hammering and polish- 

 ing, formed to the parabolic curve of a mould made with ma- 

 thematical precision. The diagram for the Bell Rock reflectors 

 was drawn by Professor Leshe, and the mould was made by 

 Mr Adie the optician. The powers of this elegant production 

 of the mechanical art are quite astonishing ; and when these re- 

 flectors were examined by the late Professor Playfair, he ex- 

 pressed his unqualified admiration of the accuracy with which 

 the curve was formed. If, for a moment, we compare the highly 

 polished and regularly curved surface of the silvered copper re- 

 flector with the few corresponding points of the parabola formed 

 hy Jacettes of glass, the superiority of the former seems to be 

 quite infinite. But what can be more authoritative than the 

 fact that their influence completely extends to the horizon form- 

 ed by the height of the light-house tower and the earth's cur- 

 vature ? The lights, for example, of Sumburgh Head and 

 Cape Wrath are seen from a ship's deck at the distance of 

 nine leagues at sea. Both the light of the natural appearance 

 and that which is coloured red at the Bell Rock are seen at 

 the distance of thirty-five miles from an elevated situation. Ob- 

 servations have also been made across the Frith of Clyde from 

 Wigtonshire to the ]\lull of Kintyre, a distance of thirty miles, 

 from which Corsewell hght is seen, though it presents only three 

 reflectors to the eye of the observer ; and Inchkeith light, with 

 only one reflector upon a face, is seen as a good sea-light at the 

 distance of twelve or fourteen miles. 



In the early state of the Northern Light-houses, whale-oil and 

 the common lamp were in use ; but, in their improved condition, 

 spermaceti oil and the Argand lamp have been introduced. 

 We believe it has been proposed by some to introduce oil-gas 

 in a portable form for hght-house purposes; but we take leave 



VOL. XV. NO. XXIX. JULY 1833. H 



