RECENT EXPERIMENTS ON FOG-SIGNALS 269 



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 strengthen- 

 ing 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 

 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 in- 

 debted 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 max- 

 imum number of jets being 824. 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 inven- 

 tion. 



The last great agent employed in lighthouse illumination 

 is electricity. It was in this Institution, beginning in 1881, 

 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 

 Faraday's words have a prophetic ring. *' I have rather, ' * 



