A TALK ABOUT LIGHTNING. 35 
metals are practically available, namely copper and iron, the first of these- con- 
ducting electricity about eight times as well as the other. Copper, then, is the 
best material. Next to copper ranks the so-called ‘‘ galvanized iron,” iron coated 
with zinc. The latter metal not only conducts better than iron, but protects the 
iron from rust. Common iron is the worst material of the three. The size of the 
rod is the next consideration. If copper alone is used, a half-inch bar will carry 
off any stroke which is ever likely to fall in our latitudes. Of galvanized iron a 
three-fourths inch rod should be used, but of common iron nothing less than an 
inch in diameter is a perfect protection. ; 
Now, how shall the rod be constructed? Here we come into collision with 
certain popular whims. It is common to see rods carefully separated from the 
buildings they are intended to protect by neat little insulators of glass. These are 
utterly useless. An electrical spark which could break through the thousand or 
more feet of air intervening between the earth and the clouds would pay but little 
respect to the inch or so of space occupied by the insulator. Besides, if the path 
of least resistance lies in the lightning-rod the flash will not leave it for any more 
difficult channel. Another popular whim concerns the shape of the rod, many 
people having an idea that a spiral form is the best. This is a matter of no im- 
portance, and need be considered no farther. Let us begin at the tip of our rod. 
This needs to be protected from rust, and also to some extent against fusion. The 
latter difficulty may be gotten over by forking the tips, so that a flash falling upon 
it shall be divided into several parts. The other object is to be attained in several 
ways. ‘The tip may be made either of platinum or aluminum, or it may be plated 
with nickel, or simply gilded. The last-named plan is the best and cheapest. The 
gilding costs but little, does not tarnish, and affords a surface of actually higher 
conducting power than either iron, aluminum, platinum, nickel, or zinc. Gold 
ranks next to copper in the scale of conductivity, silver standing at the head of 
the list. A silver tip, however, would be bad, for many reasons which need not 
be given here. As regards the body of the rod, this should be perfectly continu_ 
ous throughout. No breaks should occur in it. Wherever joints are necessary 
the continuity of the conductor should be preserved by soldering. The lower 
extremity of the rod must be arranged with great care, and ought to extend sey- 
eral feet beyond where it leaves the building. If possible, it should terminate in 
a spring, well, or sheet of water, by means of which the electric shock may be 
scattered and lost. But by no means ought it to dip into a closed cistern or cesspool. 
A discharge of lightning, prisoned in such a place between stone walls, will send 
them asunder in order to escape. Ordinarily it is well enough to divide the lower 
extremity of a rod into several branches, and allow them to run about four feet 
deep into moist earth. By making the rod terminate directly under the water- 
spout, the earth into which it plunges may be thoroughly drenched at every 
shower. Another good plan is to fill a pit with several bushels of charcoal, 
which, previously heated to redness, has been suddenly quenched. The forked 
termination of the conductor is then buried in this pit. But such precaution is 
needed only where there is but very little moisture in the soil. 
