54' BOARD OF AGRICULTURE. 



not be avoided they should be made by screwing the parts firmly 

 together by a coupling ferule, and should be rendered water tight. 



4th. It is sufficient that the rod terminates in a single point, 

 although multiple points are frequently employed. The point 

 which must be sharp, should be encased with platinum. This 

 casing will not only protect the point from the action of the 

 weather, but if of sufficient thickness, (one-twentieth of an inch) 

 will insure against liability of melting from any probable electric 

 discharge. 



5th. The rod should .be fastened to the building by iron eyes. 

 Cylinders of glass are generally used for insulators. They are of 

 but little service, especially after they have become wet with 

 water. 



6th. Acute angles made by bending the rod should be avoided. 

 The more direct the communication with the earth the better. 



1th. The gravest errors are sometimes made in establishing 

 the connection with the earth. "The rod should be connected 

 with the earth in the most perfect manner possible ; and in cities 

 nothing is better for this purpose than to unite it in good metallic 

 contact with the gas-mains or large water pipes in the streets ; 

 and indeed, such a connection is absolutely necessary, if gas or 

 water pipes [are in the house. Electricity, by what is called in- 

 duction, acts at a distance on the perpendicular gas pipes within 

 a house, rendering them so highly negative, the cloud being posi- 

 tive, as to attract the electricity from a lightning rod imperfectly 

 connected with the earth, or even from the air through the roof. 

 Damage to buildings on this account is of constant occurrence. 

 The above connection can be made by soldering to the end of the 

 rod a strip of copper, which, after being wrapped several times 

 around the pipe is permanently attached to it. Where a con- 

 nection with the ground cannot be formed in the way mentioned, 

 the rod should terminate, if possible, in a well, always containing 

 water ; and where this arrangement is not practicable, it should 

 terminate in a large plate of iron or some other metal buried in the 

 moist ground. It should, before it descends to the earth, be bent 

 so as to pass off nearly at right angles to the side of the house, 

 and be buried in a trench surrounded with powdered charcoal." — 

 (Prof. Joseph Henry.) 



8th. Large masses of metal within the building, particularly 

 those that are vertical in direction, should be connected with the 

 rod. 



