8 14 THE POPULAR SCIENCE MONTHLY. 



however, a galvanized iron rod conducts as a combination of iron and 

 zinc, in which the zinc possesses a much higher conducting power than 

 the iron. Zinc surpasses iron in this particular at least three times. All 

 the statements of conductivity that have been drawn from galvanized 

 iron conductors have hence been given much too low. The influence 

 of a too powerful electrical discharge upon a conductor of galvanized 

 iron is, in the first instance, to strip off its coating of zinc by melting 

 this more readily fusible metal. But until this is done the zinc assists 

 very materially in the transmission of the discharge. Practically it is 

 known that galvanized iron ropes effectually transmit discharges which 

 could not be safely carried by ungalvanized ropes of the same diame- 

 ter. The table is on this account worthless for the purpose for which 

 it was avowedly prepared. It attributes to several of the authorities 

 which are named views on the matter of the size of lightning-con- 

 ductors which they would certainly not indorse. For instance, Mr. 

 Preece, the eminent electrician, is represented as holding that a copper 

 wire with a sectional area of only the one-hundredth part of a square 

 inch is " sufficient to serve as a lightning-rod for any house." The 

 authority upon which this startling statement is made is a passage in 

 the " Journal of the Society of Telegraph Engineers," in which Mr. 

 Preece says that he thinks "galvanized iron wire one quarter of an 

 inch in diameter is sufficient for the protection of any house." It 

 needs no very large amount of acquaintance with electrical matters to 

 enable the reader to understand that Mr. Preece would not himself 

 have expressed the same confidence in a small copper bell- wire such as 

 is given as the equivalent in the table of the report. Taken in con- 

 nection with the omission of all reference to the increased resistance 

 in long conductors, it might be inferred from this estimate that Mr. 

 Preece would hold a small copper bell-wire, carried from the golden 

 cross of St. Paul's to the ground, to be a sufficient protection for the 

 great metropolitan cathedral. 



In his " Notes et Commentaires sur la Question des Paratonnerres," 

 printed in 1882, Professor Melsens complains that no notice of his sys- 

 tem of numerous conductors of weak or small section has been taken 

 in the code of laws of the Lightning-Rod Conference of London, even 

 as a possible alternative of construction, a silence which he interprets 

 as equivalent to a formal condemnation. He says : 



Still, I believed that the silence which the conference observes in its code 

 of law upon tlie possible application of my system was equivalent to a con- 

 demnation ; I should have been glad to see the conference pronounce, distinctly, 

 witliout any reticence, either for or against the system as a whole, or in regard 

 to its adoption concurrently with the lightning-rods which it prescribes or 

 which it commends ; the eminent savants who were a part of it would not have 

 failed in that case to discuss the essentials, with great profit in the elucidation 

 of the scientific and practical question, particularly on tlie points still subject to 

 discussion, and on which we still meet very opposite opinions. I have to regret 

 deeply, especially in consideration of the ancient savants who are members of 



