130 
Drought of 1870 and 
in excess of the quantitj- which can be absorbed and retained 
within the pores of the soil and the upper layers of the subsoil ? 
These questions cannot be so satisfactorily answered in regard 
even to any particular soil, or season, as is desirable ; and could 
they be so, the answers would vary greatly with variations of soil 
and season. As already stated, direct experiments are now in 
progress at Rothamsted with the view of acquiring useful data on 
this subject. With regard to the results hitherto obtained, it may 
be remarked that, from September 1st to December 31st, 1870, 
that is, commencing after the unusual drought of the preceding 
summer, it was found that, out of a rainfall of about l0'5 inches 
within the same period, about 50 per cent, had passed below a 
depth of 20 inches, about 40 per cent, below 40 inches, and 
about 20 per cent, below 60 inches from the surface. Calcula- 
tion further showed that, even supposing there were some accu- 
mulation during August, still, a very large proportion of that 
which did not so pass, would be required to bring the previously 
very dry soil to the point of saturation — judging this require- 
ment from the results which have been already given bearing 
upon the point. That is to say, as would be expected, a com- 
paratively small proportion of the rainfall was evaporated at that 
season of the year. Much more would, of course, so disappear 
taking the whole year round ; the quantity varying considerably 
with the characters of the soil and the season. 
Towards the end of the last century, Dr. Dalton * devised an 
apparatus for the determination of the proportion of the rainfall 
which passed off from the soil by drainage, and by evaporation, 
respectively. It consisted of a cylinder 10 inches in diameter, 
3 feet deep, open at the top, and closed at the bottom ; but 
having one small exit tube near the top, and another near the 
bottom, for the escape of water into bottles placed to receive it. 
The vessel was filled with earth, and sunk into the ground level 
with the surface, one side being left exposed for access to the 
bottles. He continued the experiment for three years, 1796-7-8, 
and found the drainage to average, over that period, 25 per cent., 
and the evaporation to be, therefore, equal to 75 per cent, of the 
rainfall. This was exclusive of any evaporation of dew, but in- 
clusive of that resulting from vegetation, as the surface of the 
soil became, after the first year, covered with grass ; a circum- 
stance which, however. Dr. Dalton considered immaterial. 
For eight years, 1836-1843, Mr. Dickinson, of Abbott's Hill, 
King's Langley, Herts,t experimented with a modification of 
Dalton's apparatus. The cylinder he employed was 12 inches 
in diameter, and 3 feet deep, but provided at that depth with a 
perforated bottom, and a receptacle beneath for the collection of 
* Mem. Lit. Phil. Soc. of Manchester, vol. v., part 2. 
t ' Journal of the Eoyal Agricultural Society,' vol. v. 
