82 NEGRETTI AND ZAMBRA, HOLBORN VIADUCT, B.C., 



POSITION FOR RAIN GAUGES 



106. From the observations made at the Royal Observatory at Greenwich, 

 the fact is clearly established that in the lower regions of the atmosphere, the 

 quantity of rain which falls diminishes with the altitude above the ground. 



The height for placing the receiving surface of a rain gauge is somewhat 

 open to a difference of opinion. Mr. Glaisher's gauge is directed to be ** half 

 sunk in the ground." This would place the edge of the gauge about 8 inches 

 from the surface of the ground. Mr. Symons gives 12 inches as most correct, 

 10 inches as a mean between these will be perhaps the best to adopt. Rain 

 gauges should be placed on a level piece of ground, and not on a slope or 

 terrace, away from walls or trees, as many feet from their base as their height, 

 the edge of the funnel should be set quite level. Unless for special observa- 

 tions Rain Gauges should not be placed on roofs or any very elevated position. 

 It is very important that Rain Gauges be occasionally examined to see that 

 the Receiving Funnel be not choked up by dust or leaves, and that at very wet 

 stations the receiving portion of this Gauge be sufficiently large to hold any 

 possible rainfall ; even the probable occurrence of a water-spout might be 

 provided for in hilly or very exposed situations. Gauges should be well 

 supported to prevent their being knocked down or blown over by the wind, 

 and after riow or frost the gauges should be placed in a warm room until the 

 collected contents are melted and can be measured. In measuring off the 

 quantity of collected rain, the graduated glass should be held quite upright, 

 and the reading taken midway between the two apparent surfaces of the water. 

 The rain should never be collected in the graduated measure, especially in 

 winter, to avoid risk of breakage by frost. 



107 Measurement of Rain. The Rain Gauge should be examined 

 every day, at nine a.m., and the amount of water collected by it entered in the 

 register, as having fallen on the previous day ; for if we measure at nine a.m. 

 to-day, it is probable, under ordinary conditions, that more of the Rain 

 collected by the Gauge will have fallen during the fifteen hours of the previous 

 day up to midnight than during the nine hours extending from midnight to 

 nine o'clock of the following morning. 



A vast amount of interesting and most valuable information respecting 

 Rain Gauges and the Rainfall will be found in Negretti and Zambra's Treatise 

 on Meteorological Instruments, and Mr. G. J. Simons' eminently useful 

 publications as enumerated in our list of books at the end of this section. 



