HI.] 



RAIN AND DEW. 



49 



London, as 33"86 inches in 1872, and only 22-6'j inches in 

 1873. But striking as the difference is here, it is yet more 

 marked in other localities. At Bamsley, for example, the 

 fall in 1872 was 42'28 inches, and in 1873 only i5'9 inches; 

 in other words, the rainfall in the dry year was but 38 per 

 cent, of that of the preceding year. 



It may be useful, before quitting the subject of rain, to 

 explain how the rainfall at any given station may be 

 determined. Although the operation is extremely simple, 

 numerous kinds of rain-gauge have been devised. The 

 accompanying figure (Fig. 12) represents a simple form 

 recommended in the Instnictio?is in the use of Meteorological 

 Instruments (1875), compiled by Mr. R. H. Scott, director 

 of the Meteorological Office. The in- 

 strument consists of little more than a 

 circular metallic funnel for catching the 

 rain, and a vessel for storing it. All 

 the rain which falls upon the open 

 mouth is collected, and, when collected, 

 is exposed to but little loss by evapora- 

 tion. The area of the collecting vessel 

 varies in different forms of apparatus, 

 the Meteorological Office employing a 

 funnel eight inches in diameter. By 

 means of the high cylinder around the 

 top of the funnel, snow may be collected; but there are 

 great difficulties in making accurate observations on the fall 

 of snow. It is notable that different amounts of rain will be 

 collected by gauges placed at different heights in the same 

 locality ; a gauge at a low level always reading higher than 

 one above. In all cases the instrument must, of course, be 

 placed in a freely-exposed situation. Every morning, at nine 

 o'clock, the rain collected during the preceding twenty-four 



£ 



Fig. 12. — Rain-gauge 



