WEATHERCOCKS.
Although such an opinion seems scarcely orthodox, it may, and not
unreasonably, be doubted whether weathercocks are of any great use in
demonstrating the direction of the wind. The under-currents of air are
so numerous and so conflicting--especially in towns where the houses
are lofty--that it is quite possible for two weathercocks at different
ends of the same street to show at the same moment the wind blowing
from opposite directions. However, the prevailing custom of placing
these ornaments, in connection with lightning conductors, on the
highest points of large buildings renders necessary some explanation of
the manner in which they should be fixed; for if they are improperly or
negligently attached to the lightning conductor, the continuity of the
latter may be rendered defective, or at least seriously impaired.
The two main points to be kept in view are, that the weathercock should
move freely with the wind, and that the continuity of the lightning
conductor should be preserved. One method of obtaining this result is
to put the weathercock into a circle, with the terminal rod of the
lightning conductor on the top. This is called the ‘nimbus cock,’ and
is in somewhat doubtful taste. The continuity, however, is perfect, and
the cock, which is simply placed on to a point, moves easily with the
wind. An example of this cock may be seen erected on the central finial
of the Cathedral at Amiens.
[Illustration: Fig. 5.]
A different way is to make the terminal rod of the conductor serve as
a pivot for the cock, as shown in fig. 5. This is the usual kind of
weathercock used in England, and is considered by many to be one of the
best forms. It is arranged in this manner: the actual terminal of the
conductor ends with a rounded or sharp point of steel, and acts as a
spindle, on which the weathercock revolves. It varies in diameter from
five-eighths to three-quarters of an inch. A tube, from seven-eighths
of an inch to one inch in diameter, and on which is fixed the cock, is
made to fit on to this terminal or spindle. This tube contains at the
extremity of its interior a piece of steel or glass, or sometimes a
glass ball, and being lengthened to a point, with a platinum or copper
tip, serves as the point of the lightning conductor. This weathercock
is generally called a ‘formed cock;’ it measures at its extreme length
about twenty-one inches, and weighs about twelve pounds. It will be
seen that in this method there is nowhere absolute contact between the
point and the pivot; consequently electric sparks must be caused by
the current of electricity. Besides this defect, if the metal becomes
oxidised between the surfaces, insulation will be the result. This
plan, though often adopted, sacrifices the principal for the sake of
the accessory.
[Illustration: Fig. 6.]
Fig. 6 shows another method of fixing the weathercock on to the
conductor. It is called a ‘solid cock,’ and is cut out of sheet-copper
one-sixteenth of an inch thick; it revolves on a spindle in the manner
shown in the engraving. This spindle, on which the cock or ‘blade’
works, differs in diameter according to the weight of the bird, the
height and style of the building, &c., but as a rule it is from
five-eighths to three-quarters of an inch in diameter.
It is usually used for Gothic buildings and private mansions, but
should not be adopted, as it is apt to be lifted off its spindle by
the wind. When a down-current of wind takes place there is generally
an up-current at the same time, and there is a possibility of the cock
being blown off during a gale. If it is used it should have a long
point fixed above it.
[Illustration: Fig. 7.]
A better arrangement than either of the two preceding ones is to let
the point go quite through the weathercock in an encasement. The
cock is then supported on a small round embasement, upon which are
placed three small rollers (see fig. 7); on these the vane revolves
easily, the continuity of the lightning conductor is perfect, and
the weathercock freely turns round on the point so long as the small
rollers are in order. In this arrangement, as in most others, the best
material for the point is copper. Steel has occasionally been used, but
it was found that in a very short time the rust had so eaten into the
joints that the cock would not turn with the wind.
The most complete and enduring method is that indicated in figs. 8 and
9; this is the plan adopted in England for all the best work. By this
arrangement, the friction being very much diminished, the weathercock
revolves with great ease and freedom; the possibility of its getting
out of order is reduced to a minimum; and the continuity of the
lightning conductor remains unimpaired.
[Illustration: Fig. 8.]
[Illustration: Fig. 9.]
It is accomplished in this way:--A circular plate, through the centre
of which the point passes, is permanently fixed some distance down
the point. On this circular basement rest three glass balls, rolling
on three axes radiating from the centre, i.e. the point, and fixed in
their outward extremities to a ring which surrounds the balls (see
fig. 9). On these balls is placed another circular plate, on which is
fixed the weathercock. The weathercock and circular plate, with a hole
through the centre, is simply put on to the point of the conductor, and
allowed to rest loosely of its own weight on the balls of glass.