Page:Popular Science Monthly Volume 30.djvu/834

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facts upon which these conclusions are based, remains to be worked out. Much remains to be done before we can fully understand the forces which impel and enable the bird creation to perform those long and perilous journeys across the depths of air and tracts of ocean, to seek for warmth and food in distant lands, and to return in season to their winter or summer homes.


By Professor L. R. F. GRIFFIN.

MODERN industrial operations necessarily employ great quantities of powerful explosives, of which gunpowder and some of the forms of nitroglycerin are the most important. Nitroglycerin, for convenience in handling, is now commonly absorbed, by Richmond infusorial earth, and is then known as dynamite. The use of these substances is not confined to the country, where they can be stored with comparative safety, but many engineering operations in cities require their aid to secure economical construction. This often necessitates their storage in considerable quantities, so that it becomes a source of danger. Special precautions are necessary to reduce the danger as much as possible, and to confine the effects of any accidental explosion within the narrowest limits. Usually, making the buildings used as magazines low, with strong walls and very light roofs, has been considered sufficient. Then, if explosion comes through accident, the explosive material spends its force upward, and the only damage to neighboring property arises from the shock given to the air. This plan may have been ample protection when gunpowder alone was stored, but the large substitution of dynamite in blasting has led to storing that explosive in the magazines, and a recent occurrence dangerously near Chicago has shown that it is by no means sufficient.

On Sunday morning, August 29th, Chicago and places in its immediate vicinity were startled by a sudden jar, followed by a dull thud, as of a distant gun of large size. It was sufficiently violent to shake buildings six miles distant, so that, although a very severe thunder-storm was occurring at the time, guests in some of the hotels rushed frantically down-stairs, suspecting an earthquake. Plaster fell in the Immanuel Church, more than five miles away, so that it was at first supposed to have been struck by lightning, and a large plate-glass window in the Board of Trade building, about seven miles distant, was cracked, and the clock on its tower was put back three seconds. An examination showed that Laflin & Rand's powder-magazine, one of a group of eleven, standing on a comparatively open area of some forty acres, about a mile and a half west of the village of Brighton,