VOL. LXIV.] PHILOSOPHICAL TRANSACTIONS. 557 



iron chain, which I also connecteil with a plate of metal, on which I intended to 

 make the discharge by the discharging rod, fig. 1 8. This done, I hooked 

 another chain, much longer, and of brass, to the opposite side of the jar, and 

 brought the end of it within 8-^ inches of the metal plate. In contact with this 

 end, I laid a small oak stick, 8 inches long, which I covered with saw-dust of 

 fir-wood. On making the discharge on the plate both the chains were luminous 

 through their whole lengths ; as was also the saw-dust, which was covered by a 

 streak of light, making a very pleasing appearance. From this experiment 

 may, I think, be inferred, the necessity of making the conductors, erected as a 

 security to buildings, &c. from the damage of lightning, both of the best ma- 

 terials, and of a very sufficient substance ; and for this purpose, perhaps nothing 

 will be found so proper as lead, which will remain in the earth many centuries 

 without any considerable decay ; and the tops of chimnies being covered with it,* 

 and furnished with a long, sharp pointed rod of copper, or iron pointed with 

 copper, which I think should extend at least 5 or 6 feet above the top of the 

 chimney, or highest part of the building ; a communication should be made 

 from it by plates of lead, 8 or 10 inches broad, with the lead on the ridges and 

 gutters, and with the pipes which carry down the rain water ; which pipes 

 should be continued to the bottom of the building, and there made to communi- 

 cate, by means of another leaden pipe, or a plate of it, as before mentioned, with 

 the water in a well, or the moist earth, or the main pipe which serves the house 

 with water. 



§ 4. Description and Use of a new Prime Conductor. 

 , A, fig. l6, is a glass tube, 18 inches long, and near 1 inches in diameter. 

 B, c, balls of brass, with a ferule, 2 inches long, to each of them ; which 

 ferules are to be cemented to the ends of the tube, and made air-tight. One of 

 the brass plates, which are soldered to the ferules, has a small hole drilled 

 through it, by which the air is to be exhausted. It is covered by a strong valve, 

 properly secured, and concealed by the brass ball b or c. d, e, balls of brass, 

 about 4- of an inch in diameter, fixed on wires, which project 2-4- inches from 

 the brass plates, at each end of the glass tube, f, a fine pointed wire, to col- 

 lect the electricity from the excited glass globe, &c. g, supporters of sealing 

 wax, on which the luminous conductor is to be mounted. 



N. B. The dots in the tube are intended to represent the appearance of the 

 electricity in it, described in the experiments. But when a bottle or a large jar 

 is discharged through the glass conductor, it is uniformly filled with light. 



• I mention covering the tops of chimnies with lead, as a protection to the upper covirses of 

 bricks, from the eifects of wind ; and not as being of any essential service to the conductor, any 

 farther than as it may assist in fixing the pointed rod, which is to be elevated above it, more securely, 

 — Orig. 



