42 



VETERINARY HYGIENE 



accompanied by a fall of rain. A rain gauge enables the rainfall 



to be measured. 



A gauge of the Meteorological Office type consists of a funnel of 



5 or 8 inches diameter 

 and a graduated glass 

 vessel, which thus en- 

 ables the rainfall to be 

 determined. There is 

 also another type known 

 as the Snowden rain 



gauge. 



An inch of rain fall- 

 ing on one square yard 

 is equal to 4-67 gallons, 

 and 1 inch on 1 acre to 

 110 tons. The average 

 rainfall for England 

 FIG. 4. A Rain Gauge. and Wales is approxi- 



mately 37 inches annually, for Scotland 43 and Ireland 39 inches. 

 On the west coast the fall is greater than on the east. One inch 

 a day is regarded as a heavy fall, while 4 inches on one day is 

 exceptionally heavy. 



Deiv has already been referred to under Dew Point, and consists 

 of drops of moisture deposited on cold surfaces. Blades of grass 

 may also have dew formed on them by water rising through the 

 vessels of the leaf. 



Fog, Mist, Haze. In some cases these have been taken to be 

 almost synonymous terms. The general feature is that the atmos- 

 phere is rendered partially obscure on account of the presence of 

 drops of water or solid particles. 



According to the Meteorological Glossary, a fog generally 

 implies that movement is rendered difficult on account of the 

 obscurity produced. There is a cloud present at or close to the 

 surface level which may contain smoke and dust particles, etc., 

 while a mist consists of a cloud at surface level containing water 

 droplets and a haze may arise from impurities such as dust or smoke 

 particles or variations in density of portions of the atmosphere. 



Hail refers to the falling of frozen water. In hard or true hail 

 the hailstones are hard and may in cases be large ; in soft hail the 

 product is soft and has a consistency resembling hardened snow. It 

 was proposed at a conference at Vienna to define hail as " the precipi- 

 tation of frozen water in which the stones attain such a magnitude 

 that they may be expected to do damage to agricultural products." 



