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.
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.
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.