1870.] 



Rainfall in England. 



471 



(40*5 feet), the result is an annual average deficit of *12 inch, 

 or "4 per cent., for every foot of elevation above the ground. In 

 other words, if the rainfall, received during a year by a gauge on, or 

 a few inches above, the ground, be divided into 1000 equal parts, 

 for every foot a second gauge is placed vertically above this, it will, 

 on the average, receive four such parts fewer. 



It is obvious that this uniform average " foot-defect" of "4 per 

 cent, of the receipts of the lower gauge presupposes that the lower 

 gauges are all at the same small height above the ground, and that for 

 a given depth or zone of atmosphere the actual deficit is the same, 

 whether the zone be at a high or low level. The first is unfortu- 

 nately anything but true, as some of the lower gauges are level with 

 the surface, whilst others are as much as 8 * 5 feet above it. 



Waiving this however, interesting information on the second 

 point is contained in the returns, tabulated below, from Southampton, 

 Oxford, and Preston, and which have been selected from the entire 

 list simply because they extend over a greater number of years than 

 any of the others, and because the difference in the heights of the 

 gauges, that is, the depth of the zone of atmosphere on which the 

 experiments were made, was not the same at any two of the stations. 



Stations. 



Vertical 

 gauge- 

 distances. 



Relative Foot-defects. 



1860. 



1861. 



•92 

 •59 

 •11 



1862. 



1863, 1864. 



1865. 



1866. 



1867. 



1868. 1869. 



Means. 



Southampton 

 Oxford . 

 Preston . 



ft. in. 

 18 1 

 22 9 

 49 5 



1-03 

 •64 

 •23 



1-19 

 •65 

 •32 



■91 

 •78 

 •31 



1-113 

 •81 

 •25 



1-33 

 •69 



■11 



1-04 



•86 

 •34 



•55 

 •30 

 •34 



•66 -63 



.. '28 

 •42 -26 



•93 

 •60 

 •30 



An inspection of the Table shows that whilst at each station 

 there were fluctuations from year to year, the foot-defect was 

 invariably an inverse function of the vertical gauge-distance. In 

 other words, if a series of gauges be placed vertically above one 

 another, at uniform distances, the first or lowest will receive, on 

 the average, more rain than the second, which in its turn will 

 receive more than the third, and so on ; but the difference between 

 the receipts of the first and second will be greater than that 

 between those of the second and third, and so on. 



The foregoing Table contains twenty-nine annual returns from 

 the three stations collectively. If with them we include all the 

 annual returns from stations having gauges differing in height from 

 10 to 70 feet, and form them into six groups, such that the first 

 shall be made up of those only having a gauge-distance of from 10 

 to 20 feet, the former alone inclusive ; the second, of those whose 

 distance ranged from 20 to 30 feet ; and so on to the sixth or last ; 

 we get the following Table, in which the Southampton returns just 



