148 
On the Quantity of Bain- Water, 
Nor is this all — for the knowledge acquired by means of these 
instruments, and the exposition of the results of rain and filtration 
proved by them, together with a just acquaintance with the area 
and nature of the soils of the district supplying the streams (about 
120 square miles), enabled Mr. Dickinson, two years since, to 
demonstrate the impracticability of a scheme for furnishing the 
Metropolis with water proposed to be drawn from the valley of 
the Colne, which must have inflicted irreparable injury on the 
mill-owners, at the same time that it would have proved, in all 
probability, an abortive speculation to the adventurers. Such are 
the various and often unexpected fruits of exact knowledge. It 
was Mr. Dickinson's communication of his experiments to the 
Institution of Civil Engineers last year which introduced me to 
his acquaintance, and has enabled me to apply his acquired facts 
to the subject of agricultural drainage. 
The annexed Table, No. I., contains the monthly and annual 
indications of the two gauges for the years 1836 to 1843 inclusive ; 
those of the rain-gauge being, Mr. Dickinson informs me, generally 
corroborated by another gauge kept by the Grand Junction Canal 
Company about 8 miles distant. Table II. gives the mean result 
of the eight years' observations for each month, and the whole 
period, in terms of the depth of rain which fell on the surface — ■ 
of the amount which filtered through the Dal ton gauge — and of 
that which was evaporated or again restored to the atmosphere in 
the shape of vapour — with two columns showing the proportion 
per cent, of filtration and evaporation. Table III. presents to 
view the total amount of rain which fell during each year, with 
the per centage of filtration and evaporation. And Table IV. 
illustrates the quantity of rain and the proportion of water dis- 
posed of by filtration and evaporation, during the six hotter and 
six colder months of each year respectively. To these last Tables 
I have added columns exhibiting the weight of rain in tons per 
acre, as that expression may convey to the farmer a clearer idea of 
its amount than the more usual mode of stating it in inches of 
depth. By means of this tabular analysis we shall find the phe- 
nomena, as they may be applicable to agriculture, clearly brought 
before us. 
The first important fact disclosed is, that, of the whole annual 
rain, about 42J per cent., or 1 1 iV inches ont of 26 ,V inches, have 
filtered through the soil ; and that the annual evaporative force 
is only equal to the removal of about per cent, of the total 
rain which falls on any given extent of earth 3 feet in depth 
(Table II.). 
By a closer scrutiny we learn (Table IV.) that only about 25^ 
