104 
Annual Report of the 
For the same reason, it is well to cover an iron rod with a coating 
of black paint, having for its principal ingredient, lampblack, which 
is a good conductor. 
4. The rod should terminate above in a single point , one is better 
than many. To prevent melting the point should not be too slen¬ 
der, and should he of solid platinum soldered to a copper socket 
fitted to the top of the rod. As generally made, the point contains 
so little platinum that it may be melted by a powerful discharge. 
It is important that the point be kept in perfect condition. 
Thus much as to rods themselves. We add some directions in re¬ 
gard to the manner of erecting them. The failure of conductors to 
answer their purpose, we are well persuaded, is due almost entirely 
to the imperfect manner in which they are for the most part put up. 
It is difficult to give specific directions on this point suited to every 
case. There is especial need here of a knowledge of the laws of 
electricity and the exercise of good judgment in applying them to 
the circumstances of each case. The number and position of con¬ 
ductors, connection with the earth, &c., depend on various circum¬ 
stances, such as the form, height and size of the building, the na¬ 
ture of its materials, character of the soil on which it stands, &c. 
The following directions, however, we regard of the greatest im¬ 
portance : 
1. Points should be erected on those parts of the building most 
exposed to explosive discharges of lightning, such as the most 
prominent points—on those which from the presence of iron pipes, 
or other conducting materials, are most liable to inductive action, 
on chimneys in which there are fires during the season of thunder¬ 
storms—on that side of the house towards the point from which 
these storms usually come. 
The general rule is that a rod will protect an area whose radius 
is twice its height above the building. Points should be placed 
nearer than this rule requires, especially if there is much conduct¬ 
ing material in the building. 
2. When there are two or more points on a building, they should 
all be connected together by rods on the roof, and there should be 
several conductors running to the ground. The reason is, that 
if the discharge from the cloud is too great for the capacity of the 
rod, it may divide, or if one conductor is imperfectly connected 
with the ground it may find a passage by another. 
