254 . FKAGMENTS OF SCIENCE. 



sea-horizon. In revolving lights the lenses gather up 

 the rays into distinct beams, resembling the spokes of a 

 wheel, which sweep over the sea and strike the eye of 

 the mariner in succession. 



It is not for clear weather that the greatest strength- 

 ening of the light is intended^ for here it is not needed. 

 Nor is it for densely foggy weather, for here it is in- 

 effectual. But it is for the intermediate stages of hazy, 

 snowy, or rainy weather, in which a powerful light can 

 assert itself, while a feeble one is extinguished. The 

 usual first-order lamp is one of four wicks, but Mr. 

 Douglass, the able and indefatigable engineer of the 

 Trinity House, has recently raised the number of the 

 wicks to six, which produce a very noble flame. To Mr. 

 Wigham, of Dublin, we are indebted for the successful 

 application of gas to lighthouse illumination. In some 

 lighthouses his power varies from 28 jets to 108 jets, 

 while in the lighthouse of Galley Head three burners of 

 the largest size can be employed, the maximum number 

 of jets being 324. These larger powers are invoked only 

 in case of fog, the 28-jet burner being amply sufficient 

 for clear weather. The passage from the small burner 

 to the large, and from the large burner to the small, is 

 made with ease, rapidity, and certainty. This employ- 

 ment of gas is indigenous to Ireland, and the Board 

 of Trade has exercised a wise liberality in allowing 

 every facility to Mr. Wigham for the development of 

 his invention. 



The last great agent employed in lighthouse illu- 

 mination is electricity. It was in this Institution, 

 beginning in 1831, that Faraday proved the existence 

 and illustrated the laws of those induced currents which 

 in our day have received such astounding development. 

 In relation to this subject P^araday's words have a pro- 

 phetic ring. * I have rather,' he writes in 1831, ' been 



