254 FRAGMENTS OF SCIENCE. 



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 

 strengthening of the light is intended, for here it is 

 not needed. Nor is it for densely foggy weather, for 

 here it is ineffectual. 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 indefatiga- 

 ble 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 in- 

 debted for the successful application of gas to light- 

 house 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 wea- 

 ther. 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 employment 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, be- 

 ginning in 1831, that Faraday proved the existence 

 and illustrated the laws of those induced currents 

 which in our day have received such astounding de- 

 velopment. In relation to this subject Faraday's words 

 have a prophetic ring. ' I have rather,' he writes in 



