Bko. 21.] LIGHTXIXCr CONDUCTORS. 347 



tell the farmers. We know of a fact that two barns were burned the last 

 season in Wcstelicster County, -wliicli were ])rovidud with conductors, wliicli 

 the owners thought as perfect as it is possible to make tlicm. Several cases 

 have come within our knowledge where green trees were torn 'to shivers 

 near buildings, which saved the buildings from destruction, while llghtnin '- 

 rods on the buildings touched by tlie trees did not attract or conduct the 

 fluid. 



Tiicn, as trees certainly arc protectors, let every farmer plant trees around 

 all the farmery. Tiiat they are the very best conductors we believe, but 

 they are never tall enough to protect the barn when giving off its towering 

 column of steam. 



3Ci). Matrrial of Conductors and Insulators. — If a farmer has determined 

 to erect a lightning-rod, the first and most important thing for him to be as- 

 sured of is, M'hat constitutes the best conducting material. As there are but 

 two mateiials, copper and iron, and as both are good conductore, and only 

 vary in power according to size, the choice may be regulated by the cost. 

 M. Poulet, a French scientific writer, gives the conducting power of copper 

 as five and a half to si.\ and a half times (varying with the specimens tried) 

 greater than iron. Tlien, if iron is six cents a pound and copper tliirty-si.x 

 cents, the cost would be equal for a given length of rod. Tliis is probably a 

 fair average of the difference in the conducting power, as Dr. Priestly makes 

 copper five times greater than iron, and Prof. Faraday si.x and two-fifth times 

 greater. As scientific men have calculated tliat a copper rod, to possess suf- 

 ficient conducting power, should be, for short rods, half an inch diameter, 

 and for very long ones, three fourths of an inch, it follows that none of the 

 iron rods in use are large enough, for they are generally under one inch di- 

 ameter. We believe that that is large enough, and we do not believe that 

 insulators are necessary, but that the rod sliould be in one continuous piece, 

 and if it can not be welded together on the ground where it is to be erected, 

 it should be firmly screwed together, so as to bo as nearly solid as possible. 



If tiie rod is continuous, it may be safely fastened to the building with 

 ordinary iron staples. If it is inserted deej) iu the earth, so as always to be 

 moist, tiiere is no danger about the lightning leaving it while passing from 

 the cloud to the earth, should it be attracted by the ever bright point wliidi 

 tlie rod should, and niuat, possess, to be of any practical value as an at- 

 tractor of electricity. 



Instead of insulating a rod from the house, it would add to its efliciency, 

 it' the house has a tin roof, to connect it with the conductor. It would also 

 be beneficial, we believe, to connect the conductor with tiie tin water-si)0Ut3 

 of a wooden building. 



3G7. The Area of Attraction of LiRlitnias; (onductors.— It is of mucli impoit- 

 uiice to a farmer, if he intends to protect his buildings by lightning-rods, to 

 know how far a single rod will afford jirotcction ; tiiat is, tlic area of attraction 

 over which the single briglit point of the rod is supjiosed to exercise an in- 

 fluence — so as to attract or bend a stream of electricity tVom iU course — so 



