wind direction only. For obvious reasons it should be mounted as high above ground as possible, and it should not be in the lee of anything that may affect the wind flow.
The vane used in connection with recording apparatus is 4 feet in length. The axis carries four partly overlapping cam-collars arranged so that at least one collar is in contact with the electrical recording apparatus. The latter prints a dotted line on the record sheet. If two cam-collars are in contact at the same time the intermediate direction of the wind is denoted. Thus, with both north and west cams in contact, and the pen of each recording, the direction of the wind is northwest. The adjustment of the box containing the contact apparatus should be made to the geographic meridian, and to solar and not standard time. Thus, if local time is 20 minutes faster than standard time and the date is May 27, the total correction will be 20 minutes plus 3 minutes. The sun will be on the geographic meridian at 23 minutes before 12:00 o’clock standard time, or 11:37 a.m. The shadow of the wind vane support cast on a horizontal surface will point due north when the sun is on the meridian.
Various devices are used to ascertain wind direction in times of very low velocity. A thread flown at the end of a stick fastened near the wind vane will often enable an observer to discover the direction of the wind when other evidence is absent. An ascending smoke column is swayed by a breeze too light to move a thread. The human face is exceedingly sensitive to the wind. The small boy who wets the ball of his forefinger and holds it against the air is using a method as old as the voyage of Jason in search of the Golden Fleece. Rather more uncertain is the movement of foliage. In many instances a wind vane whittled from a very thin strip of wood and perforated so as to whirl on a pin as an axis has been pretty nearly as serviceable as an expensive vane. Small vanes made of thin aluminium sheet metal, spread-tail in pattern, have answered every purpose required for ascertaining wind direction.
On the other hand, the commercial weather vane on a church steeple or a flagstaff may be an uncertain guide. Years of weathering may have rusted it fast to the spindle; and improper mounting may prevent its coming up to the wind by many degrees.
