IV. ANEMOMETERS. 693 



pressure plate. There is an arrangement by which the accuracy may be 

 tested at any time. Designed by the late 11. Ballingall, and described at the 

 general meeting of the Society, 2nd July 1874. 



2834a. Anemometer, constructed by P. Schultze (Dorpat). 



Prof. A. von Getting en (Dor pat}. 



After 50 revolutions of the Robinson's cups an electrical contact is made, 

 but only for a small fraction of a second, because after the movement of the 

 differential wheel the electrical communication is broken, but at the same 

 time prepared for the next operation. 



2835. Anemometer (statical), in case. 



Dr. G. Recknagels, Kaiser slautern (Physical Collection of 

 the Royal School of Industry}. 



The indications of the instrument are proportional to the pressure of the 

 wind. The small size of the instrument, and the ease with which its indica- 

 tions may be read off, make it specially advantageous for investigating 

 ventilation. The velocities of the first revolution are marked on the outer 

 scale ; otherwise the constants are given with the apparatus. A small 

 weight is added by way of a check ; it balances the spring suspended at a 

 mark of the hand. 



2835a. Five Anemometers. F. Darton and Co. 



2835b. Hewlett's Anemometer. Elliott Brothers. 



Consists of a copper sphere of such a diameter that the pressure of the 

 wind on its hemisphere shall be equal to the whole or any required portion 

 of a square foot ; the sphere is mounted on a vertical rod that is suspended 

 on knife edges like a balance, and registers the force and direction of the 

 wind on a slate slab or on printed forms placed in the instrument for recording 

 daily observations. 



2836. Improved Anemometer of Combe. 



fferm. Recke, Freiberg, Saxony. 



All axle bearings in these anemometers are of stone. The setting and 

 suspending is accomplished by pulling at one and the same knob. To facilitate 

 the readings, dials with hands are provided. The fans are of trapezoidal shape 

 and reach nearly down to the axle ; they are of mica and capable 'of adjust- 

 ment, in order to ascertain the most sensitive position. 



2836a. Improved Anemometer of Combe. 



Herm. Recke, Freiberg, Saxony. 



In the preceding the axle of the fans remains unchanged during suspension 

 inasmuch as only the dial work is moved ; in this the axle is lifted parallel 

 to itself. 



2837. Pendulum Anemometer (drawing), with explana- 

 tion. Prof- Prestel, JEmden. 



2838. Tangent Scale, for determining the mean direction of 

 the wind. Prof. Prestel, Emden. 



