IV r . ANEMOMETERS. 577 



The scale for reading off the register is prepared by observing the extent to 

 which the pencil rises for every 10, as indicated by a standard thermometer. 

 In this particular instrument it is found that for every 10 the pencil is raised 

 f of an inch ; this gives ^%-ths for each degree, and the index is accordingly 

 divided to this scale. 



IV. ANEMOMETERS. 



2828. Dynamic Anemometer for obtaining the horizontal 

 and vertical pressure of air in motion, upon inclined surfaces of 

 different forms and angles. Manufactured by John Browning 

 for the Society. 



The Council of the Aeronautical Society of Great Britain. 



This instrument is intended simultaneously to determine the component' 

 parts i.e., how much pressure is due to the horizontal, and how much to 

 the vertical of a current of air when directed against planes of different 

 areas, and of different forms, at angles varying from 15 to 90. The experi- 

 ments are tabulated in the Aeronautical Society's Eeport for the year 1871 

 (Hamilton and Co.). 



2830. Static Anemometer, for measuring the force of the 

 horizontal component of the wind, especially of gusts. 



Scottish Meteorological Society. 



Two sets of Robinson's cup anemometers are placed one above the other on 

 one vertical spindle, so that the couple tending to turn the spindle depends 

 on the force of the horizontal component of the wind, not on its direction. 

 To the spindle is attached a spring, so that the magnitude of the couple (and 

 therefore the force of the horizontal component) is measured by the angle 

 through which the spindle is turned. This is recorded by a pencil which is 

 raised and lowered by a screw cut on the spindle. The clockwork and paper 

 for recording have not been sent. Designed by Professor Crum Brown, 

 M.D., F.R.S.E., Member of Council. 



2831. Anemometer, for ascertaining pressure of wind. 



Scottish Meteorological Society. 



This anemometer acts by lengthening (not compressing). The maximum 

 result is recorded by the thread which is fixed to the rod and pulled through 

 a hole in the brass plate fixed to the side of the box. To ascertain the 

 maximum elongation which takes place, press the thread against the plate, 

 then push in the disc until the part of the thread which has been drawn 

 through the hole is again tightened, and read off the result from the graduated 

 tube. The small disc is for high winds, the large for' ight. Designed by 

 Thomas Stevenson, C.E., F.R.S.E., Honorary Secretary, and described in 

 the Society's Journal, vol. iv., p. 266. 



2832. R. Ballingall's Anemometer, for continually regis- 

 tering the pressure of the wind. Scottish Meteorological Society. 



The principle of this anemometer consists in a cistern of mercury in the 

 loft hand chamber, with a wooden plunger, which acts in connexion with the 

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

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

 general meeting of the Society, 2nd July 1874. 



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