70 Dr BREWSTER on the Construction of Polyzonal Lenses 



cal as coal-gas must necessarily be, it is not in this respect that 

 I wish at present to consider it. It is to its power of produ- 

 cing a more intense light, and a more effective system of illu- 

 mination, that I am anxious to direct the attention of the Socie- 

 ty. The advantages arising from the use of this gas may be 

 thus enumerated. 



1 . y the use of Gas, we may in many situations dispense en- 

 tirely with the use of Reflectors and of Lenses. It has been found 

 by the French Commission, that the oil-lamp with four concen- 

 tric wicks gives a light fully equal to 22 good Argand burners. 

 I have constructed a gas-burner with four concentric flames, 

 which I consider equal to that number of Argand burners ; but if 

 it should be inferior, we have only to add another flame to the 

 four. In 1759, when the Eddystone Lighthouse came out of the 

 hands of the celebrated SMEATON till the year 1803, and proba- 

 bly later, it was lighted with 24 large tallow candles, without any 

 reflectors or concentrating apparatus. Now, it cannot be doubt- 

 ed that 22 Argand burners are fully equal to 24 large tallow 

 candles ; so that a single gas burner, with four or six concentric 

 flames, is sufficient to produce the same light which was exhi- 

 bited for 35 years at the Eddystone lighthouse, and which Mr 

 STEVENSON informs us *, was seen at the flag-staff of the fort near 

 Plymouth. If this single burner, however, should not be found 

 sufficient, we have only to place beside it a second, a third, and 

 even a fourth, and we may convert it into a distinguishing light 

 by the revolution of coloured, opaque, and lenticular screens. 



The expence of this flood of gas-light, emanating from four 

 burners, with from four to six concentric flames, or from one 

 burner with from 12 to 15, will, from the cheapness of coal-gas, 

 be not much, if at all, greater than that of 24 tallow candles. 



* Edinburgh Encyclopedia, Art. LIGHTHOUSE, Vol. XIII. p. 10. 



