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154 same thing should happen in the case of incandescent bodies on the surface of the earth. He at once accepted the inference, and agreed to subject his theory to this test, if matter rare enough could be found and made visible. The extremely rarefied air left in the vacuum of an air-pump, was taken as the test; and a heated plate was employed to repel this matter. The difficulty was to make the repulsion visible. This was effected by passing an electric discharge through the exhausted receiver. The air was made palpable by means of the stratified light produced by a powerful coil. Several distinguished physicists hold the point demonstrated, though, as yet, most withhold their assent.

If this new law be established, it will be the most important advance since the time of Newton. It will, indeed, dethrone gravitation from the sole sway which it has hitherto exercised. Newton's law has been repeatedly put to the test, and more than once, astronomers trembled lest the whole Newtonian structure should totter and fall; but gravitation, with its simple ratio, has come forth triumphant from the severest ordeals. One trial more awaits it, and all the astronomers of European fame are ranged on one side or other of the question. The two principal parties are M. Hansen of Altona, and M. Delauny, and with one or other of these the various combatants side. The controversy raged for some time in the Academy of