EXPERIMENT STATION BULLETINS. 197 



5. Insulators. — The rod is not to be kept from the building by glass 

 or other insulators, but attached to it by metal fastenings. 



6. This regulation stands. 



7. Fixing. — Rods should preferentially be taken down the side of 

 the building which is most exposed to rain. They should be held firmly, 

 but the hofdfast should not be driven in so tightly as to pinch the rod 

 or prevent the contraction and expansion produced by changes of tem- 

 perature. 



8. In most cases it would be advantageous to support the rods by 

 holdfasts (which should be of the same metal as the conductor) in such 

 a manner as to avoid all sharp angles. The vertical rods should be 

 carried a certain distance away from the wall to prevent dirt accumulat- 

 ing and also to do awav with the necessitv of their being run around 

 projecting masonry or brickwork. 



9. Factory chimneys. — These should have a copper band around the 

 top, and stout, sharp copper points, each about one foot long, at in- 

 tervals of two or three feet throughout the circumference, and the rod 

 should be connected with all bands and metallic masses in or near the 

 chimney. Oxidation of the points must be carefully guarded against. 



10. As an alternative, the rods above the band might with advantage 

 be curved into an arch provided with three or four points. It is prefer- 

 able that there should be two lightning rods from the band carried down 

 to earth in the manner previously described. Oxidation of the points 

 does not matter. 



11. Ornamental ironwork. — All vanes, finials, ridge ironwork, etc.. 

 should be connected with the conductor, and it is not absolutely nec- 

 essary to use any other point than that afforded by such ornamental 

 ironwork, provided the connection be perfect and the mass of iron- 

 work considerable. As, however, there is a risk of derangement through 

 repairs, it is safer to have an independent upper terminal. 



12. Such ironwork should be connected as indicated below in sug- 

 gestion 3. In the case of a long line of metal ridging a single main 

 verj:ical rod is not sufficient, but each end of the ridging should be directly 

 connected to earth by a rod. Where the ridge is nonmetallic a horizontal 

 conductor (which need not be of a large sectional area) should be 

 run at a short distance above the ridge and be similarly connected to 

 earth. 



13. Material for rod. — Copper, weighing not less than 6 ounces 

 per foot run, and the conductivity of which is not less than 90 per 

 cent of that of pure copper, either in the form of tape or rCpe of stout 

 wires — no individual wire being less than Xo. 12 B. W. G. Iron may 

 l>e used, but should not weigh less than 214 pounds per foot run. 



14. The dimensions given still hold good for main conductors. Sub- 

 sidiary conductors for connecting metal ridging, etc., to earth may with 

 advantage be of iron and of smaller gage, such as No. 4 S. W. (J. 

 galvanized iron. The conductivity of the copper used is absolutely un- 

 important, except that high conductivity increases the surges and side 

 tiashes, and, therefore, is positively objectionable. It is for that reason 

 liiat iron is so much better. 



15. Joints. — Although electricity of high tension will jump across 

 bad joints, they diminish the efficacy of the conductor, therefore every 



