METEOROLOGY. 7 247 
replacing the points by a better conducting metal, as copper or brass, cannot 
always avert this result. 
The various arrangements employed for lightning rods may be divided 
into three classes: 1. Conductors of metal strips , 2. Conductors of metallic 
wire ; and 3. Conductors of iron rods, Furthermore, we distinguish in 
each conductor three principal portions: the highest part where the light- 
ning discharge is received ; the middle part ; and the inferior portion, or the 
end. Reimarus advises to carry a continuous metallic strip along the comb 
and eaves of the roof, across the gable ends, up the chimneys, and down the 
corners of the house. For this purpose, sheet lead of the proper thickness is 
very well adapted. In this case a special pointed conductor is not neces- 
sary. Reimarus recommends its use only in the case of thatched roofs. 
Should rods be deemed necessary, they must, according to him, be erected 
at the most exposed places, especially the chimneys and gables, to a height 
of about four feet, without points, and of at least three quarters of an inch in 
thickness. The communication between the strips of lead just mentioned 
and the ground, may best be established by means of copper or lead strips, 
about three inches wide, nailed to wood. To prevent the oxydation of the 
metal, it should be covered with a good coat of oil paint. It is unnecessary 
to separate the conductor from the building by iron or wooden pins or 
clamps. It is not advisable to inclose the conductor in the masonry or 
other inner portion of the building. The lower end of the conductor should, 
if possible, dip into open, and, indeed, running water, to assist in the diffusion 
of the electricity. When the extremity of the conductor leads into a 
covered channel of water, the inflammable gas which sometimes is present 
may be set on fire by the lightning, thus producing an explosion. It is 
advisable to have the conductor end in several branches, to multiply the 
points of egress. The conductors of vessels are best constructed of thin 
brass chain, or still better, of copper, linked together in joints of about six or 
eight inches long. 
Saussure recommended conductors of brass wire. They have been 
extensively employed in Bavaria, without presenting any very pre-eminent 
advantages. Conductors of iron rods are not only the longest known, but 
also the most generally used. The Academy of Sciences at Paris, together 
with most French philosophers, recommend them above all others. 
Professor Henry has suggested a very simple and effectual method of 
protecting a house, without much expense. It consists in employing the 
spouting as part of the conductor, by having the projecting rod connected 
with the gutter above, and leading a thick wire or iron rod from the lower 
end of each spout to running water or other good conductor. As most 
houses have a system of gutters along all the eaves, connected with the 
ground by several spouts, it would seem that this is an excellent, safe, and 
economical plan. 
According to Pouillet, every lightning rod must consist of two essential 
portions, a pointed metallic rod projecting in the air, and a good conductor 
connecting the rod with the ground. To be of the greatest efficacy, the rod 
must terminate in a very fine point. The connexion with the ground must 
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