DESTRUCTIVE EFFECTS OF LIGHTNING 309 



over his heart? It would have expedited matters, and made them still more simple." 

 Richmann, of St Petersburg, had just before been killed while apparently in far less 

 danger than Dr McFait, and other incautious experimenters have since similarly 

 suffered. 



The destructive effects of lightning are familiar to all of you, so that I need 

 not spend time in illustrating them on a puny scale by the help of Leyden jars. 



All the more ordinary effects can thus easily be reproduced on a small scale. 

 How small you may easily conceive, when I tell you that a three-foot spark is 

 considered a long one, even from our most powerful machines, while it is quite 

 certain that lightning flashes often exceed a mile in length, and sometimes extend 

 to four and five miles. One recorded observation, by a trustworthy observer, seems 

 to imply a discharge over a total length of nearly ten miles. 



When a tree is struck by a violent discharge it is usually split up laterally into 

 mere fibres. A more moderate discharge may rupture the channels through which 

 the sap flows, and thus the tree may be killed without suffering any apparent external 

 damage. These results are usually assigned to the sudden vaporisation of moisture, 

 and the idea is probably accurate, for it is easy to burst a very strong glass tube, 

 if we fill it with water and discharge a jar by means of two wires whose extremities 

 are placed in the water at a short distance from one another. The tube bursts 

 even if one end be left open, thus showing that the extreme suddenness of the 

 explosion makes it act in all directions, and not solely in that of least resistance. 

 When we think of the danger of leaving even a few drops of water in a mould 

 into which melted iron is to be poured, we shall find no difficulty in thus accounting 

 for the violent disruptive effects produced by lightning. 



Heated air is found to conduct better than cold air, probably on account of 

 the diminution of density only. Hence we can easily see how it is that animals are 

 often killed in great numbers by a single discharge, as they crowd together in a 

 storm, and a column of warm air rises from the group. 



Inside a thundercloud the danger seems to be much less than outside. There 

 are several instances on record of travellers having passed through clouds from 

 which, both before and after their passage, fierce flashes were seen to escape. Many 

 remarkable instances are to be found in Alpine travel, and specially in the reports 

 of the officers engaged in the survey of the Pyrenees. Several times it is recorded 

 that such violent thunderstorms were seen to form round the mountain on which 

 they were encamped that the neighbouring inhabitants were surprised to see them 

 return alive. 



Before the use of lightning-rods on ships became general great damage was 

 often done to them by lightning. The number of British ships of war thus wholly 

 destroyed or much injured during the long wars towards the end of the last and 

 the beginning of the present century is quite comparable with that of those lost 

 or injured by gales, or even in battle. In some of these cases, however, the damage 

 was only indirectly due to lightning, as the powder magazines were blown up. In 

 the powder magazine of Brescia, in 1769, lightning set fire to over two million 

 pounds of gunpowder, producing one of the most disastrous explosions on record. 



A powerful discharge of lightning can fuse not only bell-wires, but even stout 



