5 44 THE POPULAR SCIENCE MONTHLY. 



Prof. Richmann, arranged an apparatus to collect this electricity. 

 On the first occasion of a storm he went to his laboratory to ob- 

 serve the effects. A ball of fire was seen to leap from the appa- 

 ratus to his head, and he fell lifeless. 



A flash of lightning really consists of a discharge between two 

 objects, say two clouds, or a cloud and the earth, oppositely elec- 

 trified, the charges on which suddenly combine, with the mani- 

 festation of light and heat. Lightning conductors are contrivances 

 by which the electricity of the earth is allowed to escape quietly 

 into the atmosphere, where it meets with electricity of the oppo- 

 site character from the clouds, and the two neutralize each other 

 quietly, without any explosive discharge, or, in other words, with- 

 out lightning. I need not go back to the first principles of elec- 

 trical science and explain why it is that electricity passes most 

 easily through metals, and escapes with greater freedom from 

 sharp points than from rounded knobs. Assuming these ele- 

 mentary facts, I may say that on any object, such as a house or 

 other building, the electricity tends to accumulate itself on all 

 projecting portions of the roof, etc., and especially on the highest 

 points of it. The ideal complete lightning-rod system would call 

 for a sharp-pointed copper rod erected at each of these projecting 

 pinnacles, and rising above it, and would then connect all these 

 separate points by copper rods, and eventually carry down a stout 

 copper rod to the earth. Care must be taken that due attention 

 is paid to certain main precautions : (1) The point of the conductor 

 must be kept sharp ; (2) the section of the conducting rod must 

 be sufficient to allow the electricity to pass along it ; (3) the rod 

 must be perfectly continuous ; and, lastly (4), the rod must be effi- 

 ciently connected with the ground. 



1. The sharpness of the point is insured by gilding it or coating 

 it with some metal which resists oxidation. - 



2. As to the section of the rod, a bar half an inch in diameter 

 is sufficient for all ordinary buildings. Bars are not usually em- 

 ployed, as it is difficult to bend them over cornices, etc. ; accord- 

 ingly, either wire ropes or tapes are taken. The wire ropes are 

 more liable to corrosion from wet getting in between the strands 

 than are tapes, so that the latter are generally preferred. 



3. The continuity of the metallic connection from the highest 

 point of the rod to the ground can only be secured by having as 

 few joints as may be, and by making those joints as true and firm 

 as possible by soldering. The joints should be examined from 

 time to time, for it is often found, on examination of old con- 

 ductors, that while the copper wire or tape is quite sound along 

 its straight reaches, at the bends or joints corrosion has set in. 

 As a chain is no stronger than its weakest link, a corroded con- 

 ductor, such as has been described, is perfectly useless. 



