490 ROUGH WAYS VADE SMOOTH. 



pietation of such phenomena. I am satisfied that there 

 is no exaggeration in a passage which appeared recently in 

 the ' Table Talk ' of the Gentleman's Magazine, describing 

 an account of the electric light as obtained from some new 

 kind of gas, carried in pipes from central reservoirs, and 

 chiefly differing from common gas in this, that the heat 

 resulting from its consumption melted ordinary burners, so 

 that only burners of carbon or platinum could be safely 

 employed. 



I do not propose here to discuss, or even to describe 

 (in the proper sense of the word) the various methods of 

 electric lighting which have been either used or suggested. 

 What I wish to do is to give a simple explanation of the 

 general principles on which illumination by electricity de- 

 pends, and to consider the advantages which this method of 

 illumination appears to promise or possess. 



Novel as the idea of using electricity for illuminating 

 large spaces may appear to many, we have all of us been 

 long familiar with the fact that electricity is capable of 

 replacing the darkness of night by the light of broad day 

 over areas far larger than those which our electricians hope 

 to illuminate. The lightning flash makes in an instant every 

 object visible on the darkest night, not only in the open air, 

 but in the interior of carefully darkened rooms. Nay, even 

 if the shutters of a room are carefully closed and the room 

 strongly illuminated, the lightning flash can yet be clearly 

 recognised. And it must be remembered that though the 

 suddenness of the flash makes us the more readily perceive 

 it (under such circumstances, for instance), yet its short 

 duration diminishes its apparent intensity. This may appear 

 a contradiction in terms, but is not so in reality. The per- 

 ception that there has been a sudden lighting up of the sky 

 or of a room, is distinct from the recognition of the actual 

 intensity of the illumination thus momentarily produced. 

 Now it is quite certain that the eye cannot assign less than a 

 twenty-fifth of a second or so to the duration of the light- 

 ning flash, for, as Newton long since showed, the retina 



