=126. Whewell's Anemometer.=--This apparatus, the invention of the celebrated Dr. W. Whewell, registers the horizontal motion of the air with the direction. Its mechanism may be described in general terms, as follows:-- A horizontal brass plate is attached to a vertical spindle, which passes through the axis of a fixed cylinder, being supported by a bearing at the lower end, and working in a collar at the upper. A vane is attached, by which the plate is moved about according to the direction of the wind. A fly, having eight fans, each fixed at an angle of 45 deg. with the axle, is placed upon the plate so that the axle is in the line of direction of the vane. An endless screw on the axle turns a vertical wheel having one hundred teeth, the axle to which has also an endless screw working into a horizontal wheel, having a like number of teeth, and which communicates motion to a vertical screw fifteen inches long. On this screw is placed a moveable nut, which carries a pencil. Round the cylinder is wrapped daily a paper divided for the points of the compass. The wind acting upon the vane will cause the plate to turn; and the screw which carries the pencil will travel with it, so that the pencil will mark upon the paper the direction of the wind. The fly will also be set in motion, and thereby the nut upon the screw will descend, so that the attached pencil will trace a vertical line upon the paper. When the fans on the axle are 2.3 inches from axis to end, and 1.9 inches wide, and the thread of the screw such that forty-five revolutions will cause the nut to descend two inches, 75.85 miles of wind will cause the pencil to descend through a vertical space of two inches; but the actual trace upon the paper will be longer in proportion to the magnitude of change of azimuth, or direction, of the wind. =127. Osler's Anemometer, and Pluviometer.=--Mr. Follet Osler is the inventor of a self-recording apparatus which registers the direction and pressure of the wind, and the amount and duration of rain, upon the same sheet of paper. His apparatus has met with very much approbation, and has been erected in many observatories. The mechanism may be modified in various ways, and the following is a description of the simplest and most recent arrangement. [Illustration: Fig. 89.]