the innumerable threadlets [of water], divided and subdivided like the fibers of a root."
In conclusion, it is gratifying to be able to state that all opposition to the reboisement law is in France a thing of the past. The credits voted for the first ten years were at the rate of only two hundred thousand francs a year. Now nearly twenty times as much is readily obtained by the forest administration. The total annual outlay upon the state forests is about twelve million francs, but the direct revenue derived from them is more than three times that sum, besides the vastly greater incidental advantage of building up the agriculture, commerce, manufactures, health, and general prosperity of the restored regions, to say nothing of the diminished expenditure needed to replace roads, bridges, and other structures formerly destroyed by the torrents. How much longer shall we refuse to heed what the experience of other countries teaches with regard to the treatment of forests?
In the recent Ohio floods the States which suffered most — Ohio, Indiana, and Illinois — were not those where most of the deforesting was done which caused the floods. The Hudson's head-waters are almost all in New York, and it is in the power of her Legislature to provide the needed safeguards.
By JOHN TROWBRIDGE.
PROFESSOR OF PHYSICS, HARVARD UNIVERSITY.
THE conjunction of the meeting of the American Association with the opening of the Electrical Exposition and the sittings of the National Electrical Congress leads me to say a few words upon a question which we all ask ourselves, and to which we have hitherto had no response: "What is electricity?"
After I have concluded, you will probably still ask yourselves, "What is electricity?" All I can hope to do is to make you ask yourselves the question with more humility, and a greater consciousness of ignorance; for the ignorant man, I have found, is generally sure that he knows what electricity is; and, the more learned a person is, the more he is convinced that he does not know what electricity is.
There is an advantage in sounding the depths of our ignorance, and in surveying, even from a small Mount Pisgah, the paths we have traversed, and the great promised land which lies before us. In the beginning I must express my conviction that we shall never know
- Address before Section B, of the American Association for the Advancement of Science, Philadelphia, September 4, 1884.