Page:Popular Science Monthly Volume 17.djvu/364

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tant researches on this subject, and has shown that, even if the dust of coal is not directly inflammable, it becomes very combustible when the atmosphere contains traces of carburetted hydrogen. Other dusts are directly combustible, and sometimes produce genuine catastrophes by the fact of their suspension in the air. In 1869 a sack of starch was accidentally thrown down from the top of a staircase in the Rue de la Verrerie, Paris; it burst and scattered through the air a cloud of dust which took fire from the contact with a gaslight at the bottom of the stairs, and caused an explosion. M. Berthelot has observed that special conditions of mixture are required for the actual production of such explosions, and that a hundred cubic metres of air, containing about thirty kilogrammes of oxygen, will completely burn twenty-seven kilogrammes of starch-powder, or eleven kilogrammes of coal-dust. The terrible explosion in the flour-mills at Minneapolis, Minnesota, in May, 1878, was of a similar nature with the explosion of the starch in the Rue de la Verrerie.


PREHISTORIC Archæology, the latest-born of the sciences, like her elder sister Geology, has lived through the successive stages of scornful denial, doubt, and unwilling assent, and has finally won for herself substantial recognition. The "antiquity of man" is now an established fact. Even its most strenuous opponents are forced to concede that there are proofs of his existence during a lapse of time far exceeding the limits of the previously approved chronology. For somewhat of the suspicion with which this result has been received, certain of its advocates may have themselves to blame. "Where absolute chronological determinations were of necessity impossible, and where, even at the present stage of the investigation, only general approximations can be reached, it was at least injudicious to startle received opinions, and to arouse prejudices, by asserting for mankind an antiquity of hundreds of thousands of years. Moreover, the great name of Cuvier was held up as a barrier in the path of those who claimed to have discovered proofs of man's existence under geological conditions differing from the present. Cuvier, however, never denied the possibility of finding "the fossil man"; he only questioned the sufficiency of the evidence of his existence which had been brought under his notice, and with great reason, in view of the numerous instances in which pretended fossil human bones had turned out to be those of animals, or even merely natural formations.

Many have been the definitions given of the term "fossil"; but