812 THE POPULAR SCIENCE MOXTIILT. 



Beyond that area the movement of the air was toward the point of the 

 explosion. This was shown by the forcing of the glass outward in all 

 of the more distant buildings, while the walls of at least one dwelling- 

 house and of several of the magazines left standing were thrown down 

 toward the wrecked magazine. Furthermore, the roof of one magazine 

 was clearly lifted, and allowed to drop, besides being riddled with 

 stones. These phenomena pointed clearly to diminished pressure of 

 the external air produced by the explosion, as is noticed in a small way 

 when any gun is fired. Since most of the magazines stood in this 

 region, no blow was struck upon them, and there was nothing to ex- 

 plode the dynamite stored within, else the first explosion would have 

 been followed by others in a series, and the damage multiplied. 



These phenomena taken together seem to indicate the following as 

 the steps by which the destruction was produced, though they followed 

 so quickly that only delicate instruments would have distinguished 

 them : First, the lightning exploded some of the black powder. The 

 blow produced by this explosion detonated the dynamite, tearing up 

 the ground to make the hole and breaking the foundation-stone into 

 small pieces. Then the rest of the powder exploded, sending the frag- 

 ments away in all directions. 



It is very strange that when the danger from lightning is so well 

 known — one of the same group of magazines was exploded by light- 

 ning in 1880 — no precautions are taken by the owners for protection. 

 The magazines are low structures, some of them roofed with slate, 

 others with thin metal, in all cases very light, that they may offer but 

 little resistance in case of explosion. The total neglect of precautions 

 against lightning indicates a disregard of the known laws of electricity, 

 or else the mistaken notion that a lightning-rod, by furnishing a good 

 conductor, attracts the lightning, and thereby increases the danger in 

 place of being a safe path for the current. When such buildings stand 

 upon level ground, in open areas, they necessarily become the path of 

 any descending flash. If the electricity goes through the building it 

 becomes a source of danger, because it is likely to meet sufficient re- 

 sistance to raise the temperature above the igniting-point of powder, 

 and it must be carried completely around the powder to insure safety. 

 A network of metal rods carried over the top of those whose roofs are 

 slated, and given a sufficient ground connection, would be a complete 

 protection ; it would carry away all the electricity, usually silently. 

 To protect those with metal roofs, nothing more w r ould be required 

 than wide strips of metal from the roof itself to the ground. Of 

 course, in either case, great care must be taken to prevent scattering 

 powder on the ground within reach of the electricity as it leaves the 

 conductors. The problem of protection in this case has sometimes 

 been compared with that of the protection of tanks in which petroleum 

 is stored. This is a complete misconception. Protection of powder- 

 magazines simply requires a proper conductor to carry off the elec- 



