RAIN-GAUGE.

Wairarapa Daily Times, Volume VII, Issue 1982, 5 May 1885, Page 2

RAIN-GAUGE.

Inan article contributed to the Sydney Mail, Mr H. C. Russell gives some very valuable hints to meteorological observers oti_the use of rain-gauges. He begins by pointing put that few people are aware of the fact 1 that raising the rain gauge above the ground will cause, it to catch less-rain, and therefore its is a common thing to see it placed on a post for ornament.' 'That the rainfall registered varies 'with the height of the gauge was long ago, proved" by exhaustive experiments in' England, tho results of which Mr-Russell gives in the following figures, expressing respectively the height of gauge and the percentage of rainfall:—One foot, 100; sft, .94; 10ft, 91; 15ft, 89; 25ft, 88. ; Why an elevated gauge catches less rain ;thari one on the ground is still an open question. :■ The late Professor Jevons suggested that the difference was attribiitableio the action of the wind, which rapidly increases in velocity with elevation above the surface of the ground,.and on this point Mr Russell adds:—" Now it is known that the wind will, by. making an eddy over the mouth of the, rain-, gauge, prevent some of- the rain from falling in it;, and hence, as the stronger the wind/the ereater this. effect, the higher gauges • suffer most, There 1 is good ground for, believing that this is the true reason, why .elevated rain-gauges •catch least rain.! 1 ' The recorded rainfall is also, affected l by the diameter; of the gauge and b'y : its 'locale.'. It is. quite possible to so place*' rain-gauge that ■ it will catch 'less' than ; . half , the rain .which should-fall: into it, arid go to extremes:;theotJier i?ay; and place it where the; froiii' a wall will carry into.it far niore: than the correct quantity.- With the view, therefore, of , obtaining.results that may be ■ judged' by a. uniform standard/; Mr Russell quotes the following rules, which all observers would do well to make a note of:—1. The rain guage should be Bin in diameter. This is the size adopted at the last metorological conference for-the Australian colonies and New Zealand; it is the size generally used in England, although there the Sin guage is common enough. 2. The rain-guage should'be placed with its rim. about 12inches above'the ground, and quite level,-and; a little wooden frame placed round it to prevent the wind from blowing it over. ( If any other sized guage is used, 'the size should always be stated, The rain guage should ;he placed in an open spaco, bo that no buildings or trees may affect_the rain falling into it, ,aud if such a position is not available, it is better to put the guago high enough to secure it, because tho effect orelevatingitisknowri, while the effect of shelter is an unknown quantity. As a matter of choice, we may add, Mr Russell recommends ,the,use of the form of guage designed. by .Mr Glaisher, for many years chief in (lie Meteorological Department of Greenwich Observatory.