THE FROST AND DROUGHT OF 1905. — DOANE. 631 



The selection of a site upon which to place a ganuo is of 

 primary importance. It should be ])laced upon a Hat stretch of 

 ground, not on the face of a slope, nor on the face of a cliff, 

 nor on a house top. It is a mistake to place it on the top of a 

 dam or embankment, as the accuracy of records obtained from 

 gaug-es in such positions will be somewhat doubtful. Where 

 tlie wind is blowing at right angles to the embankment an eddy 

 will be set up parallel to the slope of the bank, which will 

 have a tendency to lift the raiii over the top of the bank and 

 produce a comparatively cahn area around the gauge. 



The volume of rain collected decreases with the height at 

 which the' gauge is place above the ground, and experiments 

 have been carried out from time to time to investigate the cause 

 of this decrease. After many heated controversies over the 

 question, it has n(nv been established that this decrease is 

 wholly due to the velocity of the wivid and the angle which the 

 rain makes with the horizon. Taking one foot above the ground 

 as representing a catch of 100, at 25 feet above the ground 

 the catch was found to equal ab:>ut 7!) uer cent. This gives 

 approximately the ratio of diminution of rain caught with the 

 increase of height. It gauges are not placed at the same level 

 above the ground much of their utility is lost, because it be- 

 comes necessary, as in the ca^o of barometic readings, to reduce 

 them to a fundamental level, and the application of such a 

 correction in rainfall work is always open to a doul)t. The rim 

 of the gauge should bn set perfectly level and one foot above 

 the ground. 



While the ])v<'('ipitation records are most valuable in com- 

 ]MUiiig the yield of our water-slu'ds, in order to determine with 

 any degree of accuracy the jjercentage of rainfall collected and 

 the ru.i-off available for water works or power the evaporation 

 should be determined. 



The value oi the rainfall for water-w^orks or ])ower-systems 

 is usually determined by the average of the two or three driest 

 years, according to the storage capacity available. 



