NATURAL PHILOSOPHY. 167 



«*2. It should have great electrical capacities; a square i-od 

 requires less metal than a round rod. 



"3. It should be perfectly continuous, i. e., it should have no 

 breaks in the connections, — no links or hooks, but a perfect 

 metallic union of every part. 



"4. It should be insulated from the building to be protected, 

 except from such masses of metal as are likely to offer other lines 

 of discharge. 



"5. It should have numerous lateral points ; one in six or seven 

 feet will answer. The more numerous these points are, the 

 gi'cater the conducting power of the rod. Besides, these lateral 

 points provide for an oblique discharge, each being as good a 

 receiving point as the higher jioint at the chimney or other prom- 

 inences. They also guard against a lateral explosion, or a divi- 

 sion of the charge, which is liable to happen in case the rod is 

 overcharged, especially if it be fastened to the house with pointed 

 stajiles ; and, in case of an ujDward sti'oke, the electric fluid being 

 discharged at so many diflferent points, no harm can possibly 

 occur. 



" 6. Its upper extremity should project freely into the air, 

 should be pointed, and may be triangular, somewhat similar to a 

 bayonet, or it may have several bi'anches. The only scientific 

 advantage in having a branching head or point for the sui^erior 

 termination is this : all points are not likely to become blunt at 

 the same time. Some have supposed that the point should be 

 magnetized ; and little needles, called " magnets," have sometimes 

 been added. But it is difficult to see the practicability of this 

 recent discovery ; for most are aware that magnetized iron or 

 steel soon loses its magnetic influence. But is there an}' truth or 

 science in this application of magnetism? If there is, we confess 

 that we have not been able to discover it in any exijeriments in 

 the laboratory ; neither can we learn that the subject has even 

 been mentioned by any wi'iter whatever on the subject of elec- 

 tricity. 



"7. The upper termination should be plated with silver or 

 gold, to prevent corrosion. 



"8. Every branch rod running to chimneys and other promi- 

 nences should have a perfect metallic union with the main rod. 



"9. In cases where metallic vane spindles, or other points, 

 exist, the conductor may commence from these, and should be 

 applied immediately to the part to be protected, and not at a dis- 

 tance from it ; and should be so applied that a discharge of light- 

 ning falling on the general mass could not possibly find its way 

 to the ground through the building by any circuit of which the 

 conductor did not form a part; that is to say, the conductor 

 should be so carried over the several parts of the building, that 

 the discharge could not fall upon it without being transmitted 

 safely by the conductor. Hence, the rod should run along the 

 whole length of the ridge, and down to the ground, at least on 

 two sides of the building. If the building is large, it should run 

 down on each corner. 



" 10. Every conductor running to the ground should terminate 



