MISCELLANY. 



121 



fused the lead-pipe connections, and set fire 

 to the gas. In another instance, that of a 

 church, provided with a lightning-rod, a 

 lightning discharge left the rod at a point 

 in close proximity to the gas-pipes, ignited 

 the gas in the vestry, and the church was 

 consumed. In a third case, the discharge 

 descended a rod on a church-steeple, and, 

 when within five feet of the ground, left the 

 conductor, pierced a wall four feet thick, 

 and disappeared in the gas-pipe under the 

 floor of the church. Sillimau's " Physics " 

 gives a similar example, where, in a church 

 in Xew Haven, the lightning has twice pene- 

 trated a twenty-inch brick wall at a point 

 opposite a gas-pipe twenty feet above the 

 earth, although the conductor, of three- 

 quarter-inch iron, was well mounted, but its 

 connection with the earth was less perfect 

 than that of the gas-pipe. 



It being established that the light- 

 ning will take the easiest track into the 

 ground, it follows, from what occurred in 

 each of the above cases, that the least- 

 obstructed path was by way of the gas- 

 pipes, with their extended ground con- 

 nections. In the first example, although 

 there was a lightning-rod on the chimney, 

 the lightning took to the rope, and, instead 

 of leaving it at the lower end for the rod, 

 which was near by, found an easier passage 

 through the air to the gas-pipes of the 

 cotton-factory, which differed from the rod 

 in having an extensive ground contact. 

 The same was true in the other cases the 

 gas-pipes furnishing a readier path to the 

 ground than the rods themselves. On ac- 

 count of the great surface contact with the 

 ground, which gas and water pipes present, 

 it has been recommended that lightning-rods 

 be connected with these, as affording an ex- 

 cellent means for the escape of the electric 

 discharge. At first glance, this might seem 

 a dangerous expedient so far as gas-mains 

 are concerned, the accidents above men- 

 tioned pointing to the danger of setting fire 

 to the gas. This accident arose from the use 

 of lead-pipe in making the connections with 

 the meter. Had the gas-pipe throughout 

 been of iron or brass, nothing of the kind 

 could have occurred. Unmixed with atmos- 

 pheric air, gas will not burn, and it was only 

 through the melting of the lead-connections 

 by the lightning that the gas was liberated 



and then ignited. Brass or iron pipes would 

 have carried off the discharge without be- 

 coming fused, no gas would have been liber- 

 ated, and no fire could have occurred. Com- 

 menting upon these accidents, Mr. Wilde 

 says : " In my experiments on the electri- 

 cal condition of the terrestrial globe, I have 

 already directed attention to the powerful 

 influence which lines of metal, extended in 

 contact with moist ground, exercise in pro- 

 moting the discharge of electric currents of 

 comparatively low tension into the earth's 

 substance, and also that the amount of the 

 discharge from an electro-motor into the 

 earth increases conjointly with the tension 

 of the current and the length of the con- 

 ductor extended in contact with the earth. 

 It is not, therefore, surprising that atmos- 

 pheric electricity, of a tension sufficient to 

 strike through a stratum of air several hun- 

 dred yards thick, should find an easier path 

 to the earth by leaping from a lightning- 

 conductor through a few feet of air or stone 

 to a great system of gas or water mains, 

 extending in large towns for miles, than by 

 the short line of metal extended in the 

 ground which forms the usual termination 

 of a lightning-conductor." 



But in the country no such system of 

 gas and water pipes is at hand the con- 

 nection of the rod with the earth must 

 therefore be made in some other way. On 

 this point Mr. Brooks remarks : " Unless a 

 hundred square feet of metal can be laid 

 in the bed of a spring or body of water, I 

 believe the building is safer without the 

 lightning-rod." The advice generally given 

 is to bury the lower end of the rod in char- 

 coal or coke. Prof. Phiu says, use coke, 

 not charcoal ; and, " whether iron or copper 

 is employed, it will be well to sprinkle the 

 coke copiously with a strong solution of 

 washing-soda, for the purpose of neutraliz- 

 ing any acids that might corrode the metal. 

 If a trench ten feet long be sunk to the 

 depth of permanent moisture, and filled to 

 a depth of twelve inches with coke, it will 

 be ready to receive the end of the rod, and 

 will furnish a path for all the electricity 

 that will ever tend to escape from the 

 clouds to the earth." 



Fonl Air. The condition of the air com- 

 monly breathed in the workshop and school- 



