. Discovery. Science. DISCOVKRY 21 WTien it is said that an inch of rain has fallen, it is meant that sufficient water has fallen to fill to over- fiovving a vessel i inch long, i inch wide, and i inch deep)—that is, a cubic inch of water has fallen on every square inch of land. Since an acre contains 6,272,640 square inches, an inch of rain on this area means that loi tons of water have fallen. For the amount fallen is 6,272,640 cubic inches ; 1728 cubic inches equal one cubic foot ; a cubic foot of water weighs 62 J lb. ; and so, by calculation, we arrive at the above result. Having decided
. Discovery. Science. DISCOVKRY 21 WTien it is said that an inch of rain has fallen, it is meant that sufficient water has fallen to fill to over- fiovving a vessel i inch long, i inch wide, and i inch deep)—that is, a cubic inch of water has fallen on every square inch of land. Since an acre contains 6,272,640 square inches, an inch of rain on this area means that loi tons of water have fallen. For the amount fallen is 6,272,640 cubic inches ; 1728 cubic inches equal one cubic foot ; a cubic foot of water weighs 62 J lb. ; and so, by calculation, we arrive at the above result. Having decided the kind of gauge to use, our next problem is to select a site as free as possible from such obstructions as buildings, trees, and walls. A good plan is to place the instrument as far away from the obstacle as the obstacle is high. The late Dr. R. H. Scott, formerly Secretary and Director of the Meteoro- logical Office, recommended that " the angle subtended in each azimuth by the nearest obstacle . . should not exceed 30 degrees, and the true bearing of the obstacle from the gauge should be carefully measured and noted in the ; In plain language, the Meteorological Office recommends that the gauge be twice the distance from the obstacle as the height of the object in question, though it must be admitted that this is not always possible in small gardens. In a desire to avoid obstruction, we must avoid the other extreme. The site must not be too exposed, nor should it be on sloping ground. The rain-gauge is best fixed into the ground by fitting its base accurately into a hole lined with cement- concrete. Meteorological Office gauges are frequently made with splayed bases, and if these are firmly embedded in cement, it is quite impossible for them to blow over. All gauges should have a capacity of 4 inches'at least, for it is possible that rain sufficient to fill a gauge of this size may fall in the British Isles in 24 hours. Indeed, falls of as much as 9 and
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