288 SCIENTIFIC RECREATIONS. 



takes place. This is what we term lightning, and under such conditions 

 electricity, though very dazzling, is harmless. It is when the cloud comes 

 near to the earth, and a discharge is released, that lightning is so dangerous 

 to persons who remain in the fields. Sometimes the discharge comes from 

 the earth to meet that from the cloud. Sheep are frequently killed by 

 ground lightning, and once, at Malvern, we had an escape from an upward 

 stroke. The back-stroke from a cloud is also dangerous. It may happen 

 that the cloud has discharged itself upon the earth many miles away, but a 

 return discharge takes place at the other end, and if that end be near the 

 -earth the consequences may be serious. As a rule, the return stroke is not 

 so violent as the first discharge. 



The colour of lightning varies very much. We have the white, the 

 blue, the violet, and red. The colour depends upon the distance and 

 intensity of the lightning, and the more there is of it the whiter the light. 

 We can illustrate the varied hues of the electric " fluid " by passing a spark 



Fig. 288. Cumulus cloud. 



through the receiver of an air-pump. If the air be rarefied, or there be a 

 vacuum, we shall perceive a blue or violet light. Therefore we may conclude 

 that the blue and violet flashes have birth in high strata of the atmosphere. 

 We have all heard how dangerous 'it is to stand under a tree during 

 a thunderstorm, or rather, we should say, when the storm is approaching us 

 nearly. The tree is a conductor, and the lightning having no better one at 

 hand will pass through the tree on its way to the earth, and if we are standing 

 .against the tree we shall be included in the course, and die from the shock to 

 the nerves while the lightning is passing through us. The best position in a 

 thunderstorm, if we are in the neighbourhood of trees, is to sit or lie down 

 on the ground some little distance from the base of the nearest tree. If the 

 tree be sixty feet high suppose, and we sit fifty feet or less from the trunk, 

 we shall be pretty safe, because the lightning will reach the tree top before 

 .it can reach us. We are protected by it as by a conductor, bad though it 

 be. Standing up in a boat during a storm is not wise. Lightning has an 

 .affinity for water, and besides, if no higher objects are near, our body will act 



