and the bricks it was intended to cement become loose. The remedy for this evil is the employment of lime from non-magnesian limestone.
This explanation of the phenomenon of incrustation is pronounced to be the correct one by the editor of the Polytechnic Review, who also approves Mr. Trautwine's proposed remedy for the evil. At the same time he offers, on theoretical grounds, a simpler remedy, which he proposes to have subjected to the test of practical experiment. This remedy is the addition of a small quantity of baryta to the water used for tempering the brick-clay. The rationale of this process we will state as briefly as possible, mainly in the author's own words: The incrustation being due to the process of soluble sulphates, caused by the decomposing action of sulphuric acid on the magnesia and lime silicate in the clay, the presence of a small amount of free baryta would either altogether prevent or at least greatly reduce the amount of this decomposition. The baryta, having a strong affinity for the free acid, would seize upon it, and with it form insoluble sulphate of baryta. Even though the free baryta did not altogether prevent the formation of the soluble sulphates, it is safe to assume that there will be present in the finished brick sufficient uncombined baryta to decompose and cement into insoluble barium sulphate such soluble magnesia and lime sulphates as may have been formed during the process of burning, so soon as these sulphates are dissolved by moisture. A like addition of baryta to mortar after it is prepared for use may reasonably be expected to check the tendency to efflorescence, except of course where the mortar, as in chimneys, is continuously exposed to the action of sulphurous vapors.
An Interesting Experiment.—A simple experiment, devised by Prof. A. M. Mayer, illustrates in a very effective way the action of the forces of attraction and repulsion on bodies freely moving in a plane, and serves to give clearness to our conceptions of molecular action. He takes a number of needles, of the size known as "number 6," and magnetizes them, giving to all the points the same polarity, say north. Then each needle is driven into a small cork float, so that it will keep the upright position in water, the eye just coming through the top of the float. If, now, three of the needles be dropped into a bowl of water, and the north-pole of a rather large cylindrical magnet be brought slowly down over them, the mutually repellant needles are made to approach one another, and then arrange themselves thus... Raise the magnet, and the needles go farther apart; lower it, and they come together again, the three needles always holding their places at the vertices of an equilateral triangle. Add needles successively, and the following arrangements will be seen, viz.:
The needles can be made to assume the arrangements shown in the second column, but these figures are not stable. So long as the magnet is held directly over them, the needles will remain in the positions indicated; but raise it, so as to let the needles go apart, and then bring it down again quickly, and in all probability the figure given in the first column will be the result. Prof. Mayer has obtained the figures up to the combination of twenty needles. He adds, in a note to the American Journal of Science: "These experiments can be varied without end. It is certainly interesting to see the mutual effect of two or more vibrating systems, each ruled more or less by the motions of its own superposed magnet; to witness the deformations and decompositions of one molecular arrangement by the vibrations of a neighboring group; to note the changes in form which take place when a larger magnet enters the combination, and to see the deformation of groups produced by the side action of a magnet placed near the bowl."
Experiments with the Electric Light.—A public exhibition was recently made in Cleveland, Ohio, of an electric-light machine