WHEN OF MOST VALUE. 173 



most wants this light. I am going to show you 

 how, by means of a little steam, I can com- 

 pletely obscure this glorious sun, this electric 

 light which you see. The cloud now obscuring 

 the light on the screen is only such a cloud as 

 you see when sitting in a train on a fine summer's 

 day ; you may observe that the vapour, passing 

 out of the funnel, casts as deep a shadow on 

 the ground as the black funnel; the very sun 

 itself is extinguished by the steam from the 

 funnel, so that it cannot give any light; and 

 the sun itself if set in the lighthouse would not 

 be able to penetrate such a vapour. 



Now the haze of this cloud of steam is just 

 what we have to overcome, and the electric 

 light is as soon, proportionally, extinguished 

 by an obstruction of this kind as any other 

 light. If we take two lights, one four times the 

 intensity of the other, and we extinguish half 

 of one by a vapour, we extinguish half of the 

 other, and that is a fact which cannot be set 

 aside by any arrangement. But then we fall 

 back upon the amount of light which the 

 electric spark does give us in aid of the power of 

 penetrating the fog, for the light of the electric 

 spark shines so far at times, that even before it 



