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:— Copper 100·00 Gold 57·40 Silver 35·60 Zinc 33·30 Brass 28·05 Iron 17·40 Platinum 17·10 Tin 16·80 Lead 9·70 Here again is a striking difference with the statements of other investigators. It seems absolutely inexplicable indeed, how it could happen that scientific men of eminence, and admitted authorities on the subject they are treating, came to vary on the electric conductivity of several of the metals. The difference is most astounding as regards silver, the conductivity of which, compared with the per cent. of copper, Professor Lenz places at 136·25, Sir Humphrey Davy at 109·10, Becquerel at 73·50, and Professor Ohm at only 35·60. The only conclusions that can be come to under the circumstances are, that the record of Professor Ohm’s results as regards silver is incorrect; or, that the relative degrees of purity of the samples of metal experimented upon by him and the other professors differed very widely. What is of more importance than this question, is the comparative rank of copper and iron. Here, it is satisfactory to find, the results ascertained by Ohm agree very nearly with the conclusions of the other investigators, it being laid down that copper has about six times the conductive power of iron.