326 Transactions of the American Institute. 



ever likely to fall upon them. Of all the well-known substances, 

 metals are the best conductors ; and even among metals there are 

 great differences in this respect ; some metals, according to Becquerel, 

 conducting nearly seventy-live times better than some others. There 

 are, however, but two metals whose claims are worth considering — 

 copper and iron. The others are too costly. 



Mr. J. B. Lyman — Would there be any advantage in combining 

 the two metals, iron and copper ? 



Mr. Phin — None whatever. We speak now of the size of the rod. 

 Great differences of opinion exist in regard to the size of rods neces- 

 sary to insure safety. The old directions by the French Academy of 

 Sciences named a rod of from one-half inch to one inch square as a 

 safe conductor. The following extract from the last report gives their 

 latest views upon this point : " A discharge of our electric batteries 

 is capable of melting several yards of very fine wire. A flash of 

 lightning is capable of volatilizing more than 100 yards of bell-wire, 

 or of the wire that is usually employed in connection with the ham- 

 mers of public clocks. In 1827, upon the packet-boat New York, a 

 surveyor's chain forty yards long, made of iron wire a quarter of an 

 inch in diameter, which served as a lightning-rod on the vessel, was 

 melted by a flash of lightning and dispersed in red-hot fragments. 

 No instance has ever occurred in which lightning has raised to a red 

 heat a bar of iron some yards long, and four-tenths of an inch square, 

 or having a section of one-sixth of an inch square. Hence a square 

 rod of iron, the sides being four-tenths of an inch, has been adopted 

 in the construction of lightning-rods." This shows that the enormous 

 conductors recommended by Professor Henry and others are unneces- 

 sarily expensive and clumsy. When copper is used the size may be 

 proportionately reduced. If iron is used, the rod should, if scraare, 

 be four-tenths of an inch on the side ; if copper, one-fourth of an inch 

 is sufficient. 



Mr. F. D. Curtis — Would there be any harm if the , measurements 

 were greater ? 



Prof. Phin — None; nor would there be any advantage ; besides, 

 the rods would be unsightly and harder to handle. The different 

 forms which have been patented are not of the slightest consequence. 

 A flat rod is more convenient than any other form. If we examine 

 the rods ordinarily found in market, and puffed by those who have 

 invented them, we shall find that, instead of being solid bars of a 

 square, round or merely flattened form, they are tubes, twisted rib- 

 bons, or bars whose cross section has the form of a star. And if we 



