anemography

[Gr. ἄνεμος (anemos) = the wind, and γραφή ( graph ) =. description. A description of the winds. IMG:content-0513.png:[blocks in formation] which a windmill twists string round an axle against pre ure; 2nd, those in which a defined surface, say of a foot square, is pre ed 211 against a spring (Fig. 1); 3rd, those in which water or some other liquid is made to stand at a higher level in one leg of an inverted siphon than in the other (Fig. 2). The anemometer now most commonly in use is more akin to the first, which also was the earliest type of the instrument, than it is to the second or the third. Four light metallic hemispheres, called from Dr. Robinson, who first employed them, Robin son's cups (Fig. 3), are made to revolve like a vane or weathercock, and are found to do so at the rate of exactly one third the velocity of the wind. The result is then recorded in pencil marks by a self-registering apparatus. Fig. 2. Fig. 3.