346 J. Henry on the Construction of Laghtning-rods. - 
being observed, that its elevation should be at least half of the 
distance to which its protection is expected to extend. It is 
safer, however, particularly in modern houses, in which a large 
mou 
we a inclosed, as it were, in a case of iron rods so connect 
e earth, would be safe from the direct action of the light- 
ning. 
10th. When a house is covered by a metallic roof, the latter 
h 
ning rods; and in this case the perpendicular pipes conveying 
the water from the gutters at the eaves may be made to act the 
es better, with the gas or water-pipes of the city. In this case, 
: ns} A 
ores survey should be made, and the best form of protection 
og which the peculiar circumstances of the case 
dmi 
