ON THE RAINFALL IN THE BRITISH ISLES. 



287 



proximation to fluchiation of rainfall, 1726 to 1865." Although unprepared 

 for the extraordinary drought between 1730 and 1762, he is not at present 

 inclined to impugn the accui-acy of the returns*. 



It wiU be seen that the drought of the years 1854 to 1864 is far exceeded 

 in intensity by that at the commencement of the century, and still fui'ther 

 by the extraordinary one previously mentioned as occurring between 1730 

 and 1762. It does not seem expedient to enlarge at any length on the 

 many remarkable features of this diagram, but rather to leave the facts 

 ready for all, and not be too precipitate in drawing conclusions. 



One satisfactory point may be mentioned, viz., that in Mr. Symons's last 

 Report the following remark was made : — " On carrying the investigation 

 back to 1800 the faU then seems to have been less than it was about 1815." 

 This wiU be seen to be amply confirmed by the present extended investigation. 



Table IV. — Ratio in groups of ten years each from 1726 to 1865, from 

 adopted mean of Table III. (Mean of fifty-one years, 1815 to 1865, at 



twelve stations = 100-0.) 



20 years. 



86-7 

 83-5 

 98-4 

 93-2 

 99-3 

 100-8 

 98-5 



20 years. 

 80-3 

 88-3 

 98-5 

 92-4 

 100-9 

 102-0 



Table IV. is an abstract of the last column of Table III., which brings out 

 very clearly the dry periods in the middle of the eighteenth, and at the 

 beginning and in the middle of the nineteenth centuries. 



One obvious use of Table III. may be mentioned, as it maynot occur to 

 every one, namely, that as these calculations are mainly based on stations in 

 the midland counties, the probable fall at any place in that district, in any 

 of the last 140 years, may be obtained by multiplying the adopted mean 

 ratio from Table III. by the mean fall at any given place, as deduced from 

 modern observations. For instance, the fii-st year in the Table 1726 is set 

 down 109 ; from modern observations we know that the mean faU in North- 

 amptonshire is about 24 inches, then 1-09 x 24=26-16 ; the observed faU 

 (26-70) was 2 per cent, greater. Fifty years later 1776 stands as 107; the 

 fall in Rutland may also betaken at 24, then 1-07 X 24=25-68 ; the observed 

 fall (27-84) was 9 per cent, greater. Another fifty years, and 1826 stands 

 as 77 ; Manchester has a mean fall of 36 inches, then -77 X 36=27-72 ; the 

 observed faU (24-91) was 8 per cent. less. 



* Since these calculations have been finished, Mr. Symons has received from Dr. 

 Barham of Truro a complete copy of the register kept at Plymouth from 1727 to 1752 by 

 Dr. Huxham ; the yearly totals and ratios are entered on Tables I. and II. so as to be availr 

 able for comparison, but in different type, because they are not used in forming Table IIL 

 Their fluciuations agree very fairly with the adopted mean values in Table III. 



