1825.) 
For the Monthly Magazine. 
Direcrions concerning the Erection 
«and Use of Licurxinc-Rops for the 
Preservation of Buildings. 
LTHOUGH there has been some 
diversity of opinion, among scien- 
tific men, respecting the most advan- 
tageous mode of constructing a series of 
metallic rods, as lightning-conductors, 
yet I never remember seeing more than 
a solitary opinion given (in a long hypo- 
thetical article in a late number of the 
Edinburgh Philosophical Journal) against 
the utility of lightning-rods, as preser- 
vatives against danger from the electric 
fluid. I shall, therefore, not take up 
any portion of your useful columns, Mr. 
Editor, in discussing theories of how 
the electric matter ought to act in mak- 
ing its passage from a cloud into the 
earth ; but assume it as an incontro- 
vertible fact, that there is a constant 
tendency towards a state of equilibrium 
between the electricity of the earth and 
that of the atmosphere: and, conse- 
quently, that a cloud highly charged 
with electric matter, passing over any 
building, tree, or other elevated object, 
will discharge its superabundance of 
electric matter, through the medium of 
such elevated body, into the earth; but 
that it will, in all cases, select the best, 
or, in other words, the most ready con- 
ductor for its transit. Accordingly, 
such buildings as have been provided 
with lightning-rods have never, perhaps, 
in a single instance, been damaged or 
thrown down by a discharge of electric 
fluid, even when covered with lead, 
copper, or other metallic roofing, when 
the conducting-rods have been made of 
sufficient extent to the size of the edi- 
fice, and carried down, without any inter- 
ruption, into the earth. 
' That the most immediate communi- 
cation and contact should exist between 
the point or head of a conducting-rod 
and the earth at its base, in order to 
secure any building from the possibility 
of danger from lightning, we have the 
authority of that eminent chemist and 
natural philosopher, M. Guy Lussac. 
In a late number of the Annales de 
Chimie is a very able report (made by 
M. Lussac, in the name of a commission 
appointed by the Royal Academy of 
Sciences), containing instructions for 
workmen and others in the erection of 
lightning-rods, or, more accurately 
termed by the French, paratonnerres. 
As the article in the Annales is much 
too long for extract here, though full of 
profound remarks and valuable sugges- 
On the Erection and Use of Lightning Conducting-Rods. 
309 
tions, I shall abridge the subject, by 
giving only the principal heads of M. 
Guy Lussac’s paper. 
The author divides the subject into 
two parts—theoretical and practical. 
With regard to the first, a few words 
may suffice, in order to place persons 
on their guard, whenever they may be 
exposed to the danger of lightning. 
The velocity with which the electric 
fluid passes through the air is estimated 
by M. Lussac at about 1,950 feet per 
second: consequently, the immediate 
vicinity of a highly-charged electric 
cloud (or, as we call them, “ thunder- 
clouds,”’) is at all times dangerous to a 
person, unless protected from its influ- 
ence by some better, or more ready 
conductor of electricity than the human 
body. 
The conducting power of iron ex- 
ceeds that of sea-water in the ratio of 
100,000; and sea-water is a better than 
fresh-water in the proportion of, at least, 
1,000 to 1. As the conducting power 
of a metallic rod appears to be nearly 
in proportion to its area, large rods will 
carry down the fluid into the earth with 
greater rapidity than smaller rods, and 
consequently afford greater protection 
to any building to which they are at- 
tached: for, in the event of a dense, or 
highly-charged cloud coming near such 
building, a greater quantity of fluid 
striking the top of the rod than can pass 
into the earth with sufficient rapidity, 
a part of it will be dispersed, and pro- 
bably damage some part of the edifice. 
As itis not uncommon for persons in 
the country, who are overtaken by a 
thunder-storm, to seek shelter under a 
tree, or hedge, it may be proper to re- 
mark, that they are there in much 
greater danger than in the open field: 
for, as trees’ become conductors of 
lightning, the person, placed in contact 
with a tree struck, would inevitably 
receive part of the shock; and any me- 
tallic substance, or implements with him, 
or about his person, would increase the 
portion of that shock. It is also worthy 
of recollection, that the danger is mate- 
rially increased if the ground at the foot 
of such tree be in a remarkably dry 
state, which is almost always the case 
during the summer, or autumnal months, 
when thunder and lightning, in our 
climate, are most prevalent. 
For the same reasons, however, that 
a person would be in greater danger 
from being in immediate contact, he 
would be in less danger at a short dis- 
tance (say twenty or thirty feet) from a 
large 
