Page:Popular Science Monthly Volume 60.djvu/102

94 This was confirmed by finding traces of zinc in a number of corpses. He enumerates many ways by which zinc was found to enter the soil, among which are the following: The drainage waters from many foundations contain considerable quantities of zinc. In all regions where zinc smelting is carried on, or where there are zinc or brass foundries, the vegetation contains zinc; this arises from the fact that the particles of zinc oxid are extremely light and are carried to great distances in the atmosphere. In one instance the effluent from a slaughter house was precipitated by an effective chemical for the purpose which was sold under the name of 'sulfate.' This precipitant was found to be a very impure zinc sulfate, containing much iron and manganese. The excess of the substance passed into the stream contaminating it with zinc, while the precipitate, consisting largely of zinc albuminate, went with the other slaughter house refuse as fertilizer. It is quite possible that much of the 'tankage,' so largely used in this country in the manufacture of fertilizers, contains no inconsiderable quantity of zinc. Where zinc is thus present in the fertilizer, it would be apt to pass in traces into the fruit raised on soil thus fertilized. It is reasonable to suppose that such minute quantities of zinc would be perfectly harmless when taken into the human system, but their detection would serve to throw unjust discredit upon American fruit growers, long after they have ceased to use zinc in any part of the evaporators with which the fruit can come in contact; at least when preparing dried fruit for the export trade, these precautions have for some time been taken.

forty years ago Maxwell pointed out the main features of the electromagnetic theory of light. This theory very soon supplanted the old mechanical wave theory, or the elastic solid theory; and now the fundamental notions in light are purely electric or electromagnetic in character. It is very remarkable, however, that aside from the change in the fundamental notions themselves the old theoretical structure remains to a very great extent unchanged and that even the old nomenclature lends itself easily to the needs of the new theory with few exceptions. The change that has followed upon Maxwell's work is very like the moving of a house from old to new foundations.

There is at the present time a prospect of a similar transfer of the entire subject of mechanics to a purely electromagnetic foundation. Every one realizes that the notions of inertia and of gravitation, and the principles involved in Newton's laws of motion are far too abstract in their nature, and as elemental notions they are far too complicated to be entirely satisfactory as a basis for the most concrete of the physical sciences. It seems that the theory of electromagnetism is to supply precisely what is needful to reduce mechanics to a more elemental basis. The change, if it come, will no doubt be similar to the change which has taken place in the theory of light; the superstructure of theoretical mechanics and even the nomenclature will remain to a great extent unaltered.

The possibility of explaining the inertia of matter electrically was first shown by Heaviside. A charged body has more momentum when moving at a given velocity than if it were not charged, and if the body is small enough in comparison with its charge all its momentum may be accounted for in this way.

The possibility of explaining gravitation was first pointed out by H. A. Lorentz, who attributes it to an excess of attractive over repulsive forces of electric charges.

A remarkable consequence of Heaviside's theory of inertia is that