810 THE POPULAR SCIENCE MONTHLY. 



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. 



A REMARKABLE EXPLOSION. 



By Professor L. R. F. GFJFFIN. 



MODERN industrial operations necessarily employ great quanti- 

 ties 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 neces- 

 sitates 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 acci- 

 dental 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 occur- 

 rence dangerously near Chicago has shown that it is by no means suf- 

 ficient. 



On Sunday morning, August 29th, Chicago and places in its imme- 

 diate 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, 



