Among a host of other investigators of the subject there stand forward, besides Sir Humphrey Davy and Antoine Becquerel, two Germans, Professors Lenz and Ohm, and another French savant, Claude Pouillet. In the opinion of many scientific authorities, especially in the United States, the experiments of Professor Lenz regarding the comparative electrical conductivity of different metals were more carefully made than any other, and are therefore deserving of the greatest credit. He had, indeed, ample means and great leisure at his disposal, making his scientific investigations under the patronage of the Grand Duke, afterwards Emperor, Nicholas of Russia, while acting as his private tutor at the university of St. Petersburg. The researches of Professor Lenz as to the comparative power of various metals to conduct the electric force were given in the following results--copper, as before, standing as the centesimal unit:—
Silver 136·25 Copper 100·00 Gold 79·80 Tin 30·84 Brass 29·33 Iron 17·74 Lead 14·62 Platinum 14·16
A comparison of the figures here given with those of Sir Humphrey Davy and of Becquerel shows that the results obtained by Professor Lenz differ from those of both the other investigators. Like Sir Humphrey Davy, Professor Lenz declared silver to be of greater electric conductivity than copper, but, on the other hand, he assigned lead a very low place, putting it under iron, instead of far above it. It is difficult to explain this wide divergence, even on the utmost allowance of purity, or impurity, of metals. As regards the most important question, from a practical point of view--that of the difference between copper and iron--Professor Lenz, it will be noticed, places iron higher in the scale than both Sir Humphrey Davy and Becquerel. Still, in his estimate also, copper was admitted to have about six times the conductive power of iron.
While, as just stated, the experiments of Professor Lenz on the electric conductivity of metals are held in the highest esteem in America, the same is the case in Germany as regards those of Professor Ohm. The latter is held to be there the highest authority on all subjects connected with the measurement of the electric force. The professor, born at Erlangen, 1787, and for many years teacher of natural history at Munich, where he died in 1854, devoted the utmost patience and an immense amount of time to the definite object of ascertaining the electric conductivity of all the metals, registering the result of his experiments in a special work, the most complete existing on the subject. According to Professor Ohm, the principal metals stand to each other in conductivity as follows:—