DEATH BY LIGHTNING. 441 



ning cleaves a cloud, appearing and disappearing in 

 less than a hundred-thousandth of a second, and the 

 velocity of electricity is such as would carry it in a 

 single second over a distance almost equal to that which 

 separates the earth and moon. It is well known that a 

 luminous impression once made upon the retina endures 

 for about one- sixth of a second, and that this is the 

 reason why we see a continuous band of light when a 

 glowing coal is caused to pass rapidly through the air. 

 A body illuminated by an instantaneous flash continues 

 to be seen for the sixth of a second after the flash has 

 become extinct ; and if the body thus illuminated be in 

 motion, it appears at rest at the place where the flash 

 falls upon it. When a colour-top with differently-coloured 

 sectors is caused to spin rapidly the colours blend together. 

 Such a top, rotating in a dark room and illuminated 

 by an electric spark, appears motionless, each distinct 

 colour being clearly seen. Professor Dove has found 

 that a flash of lightning produces the same effect. 

 During a thunderstorm he put a colour-top in exceed- 

 ingly rapid motion, and found that every flash revealed 

 the top as a motionless object with its colours distinct. 

 If illuminated solely by a flash of lightning, the motion 

 of all bodies on the earth's surface would, as Dove has 

 remarked, appear suspended. A cannon-ball, for ex- 

 ample, would have its flight apparently arrested, and 

 would seem to hang motionless in space as long as the 

 luminous impression which revealed the ball remained 

 upon the eye. 



If, then, a rifle-bullet move with sufficient rapidity 

 to destroy life without the interposition of sensation, 

 much more is a flash of lightning competent to produce 

 this effect. Accordingly, we have well-authenticated 

 cases of people being struck senseless by lightning who, 



