CHAPTER XI.

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.

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.

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.

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.

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.