46 



VETERINARY HYGIENE 



a card and leave a record. This card is divided into hours, and is 



bent into a spherical shape. 



WIND. Wind is caused by the movement of the air, and this 



movement takes place on account of the sun warming different 



regions of the earth to a 

 different degree and pro- 

 ducing differences of 

 pressure. 



The familiar wind- 

 vane gives the direction 

 from which the wind 

 comes. It should be 

 placed on a high point, 

 move easily and be un- 

 affected by stray local 

 currents. 



The speed or force of 

 the wind is determined by 

 an anemometer, of which 

 there are three general 

 types which have been 

 termed the " windmill," 



FIG. 8. Robinson's Anemometer. 



pressure tube 



and 



" pressure plate." Details of these will be found in the Observer's 

 Handbook. 



The scheme adopted in 1805 by Admiral Beaufort of estimating 

 wind force by numbers from to 12 is known as the Beaufort 

 Scale. The Meteorological Office has issued a table giving a com- 

 parison between the Beaufort Scale numbers and their velocity- 

 equivalents. The following table which is taken from the 

 Observer's Handbook also gives " descriptions of the wind force 

 intended to guide the judgment of observers."* 



* G. C. Simpson, F.R.S., Director of the Meteorological Office, has drawn up a 

 specification of the Beaufort Scale for coast use. M.O. Publication 180. 1906. 



