122 Some Account of the Northern Light-hmises, 



though contrary to the expectation of some, is yet easily ac- 

 counted for, by considering that the quantity of liglit absorbed 

 by glass of a greenish colour, is too trifling to make any appre- 

 ciable difference in the intensity of the refracted beam. In re- 

 gard to the comparative trial of the lens light with the reflectors 

 at present in use on the coast, it appeared that the lens, illumi- 

 nated with a lamp consuming the oil of 14 Argand burners, was 

 fully equal in appearance to the light of 6 or 7 reflectors, each 

 having an Argand burner ; but it is to be noticed, that the 

 French lamp consuming the oil of 14 Argand burners if placed 

 in the centre of a system of lenses, would give a light in every 

 direction equal to that of 6 or 7 Keflectors. This, however, is 

 chiefly applicable to revolving lights, in some of which only 7 

 reflectors are employed, in others 12, or at most 20, according 

 to their situation. When the Bell Rock light was first exhibited, 

 24 reflectors were in use. 



The light produced by the flame of oxygen and hydrogen 

 gases- passing over a lime-ball when exhibited in the focus of a 

 single reflector, was much more powerful than either the lens or 

 reflector when illuminated by lamps. But it also deserves no- 

 tice, that a single reflector very far surpassed the lens in brilliancy 

 and effect when the lime-ball light was exhibited at the same 

 time in the face of both. 



It had farther been suggested that distinguishing lights, simi- 

 lar to those used by the Bengal pilots, might be introduced with 

 good effect into light- houses. Bengal-lights were accordingly 

 procured from his Majesty's stores at Woolwich, on the applica- 

 tion of the Light-house Board. At the same time, Mr Steven- 

 son commissioned from London a supply of the nitrates of stron- 

 tia and baryta, by the combustion of which red and green lights 

 were produced. These were also exhibited from Gullan Hill ; 

 but the red light, in so far as the experiments have yet been 

 carried, was chiefly worthy of notice. When this substance was 

 burned in great quantity, it afforded a beautiful flash of light 

 resembling the red light of the Bell Rock light. It is to be re- 

 gretted, that during these trials, the weather did not afford an 

 opportunity of making observations during fog ; but, as before 

 noticed, the experiments are again to be resumed, when we hope 

 to give precise information as to the anomalies of some of these 

 appearances. 



