146 
On the Quantity of Rain- Water, 
at any time contain. This quantity will depend, in a well-drained 
soil, on its bibulousness or hygrometric energy. If an instrument 
could be contrived to indicate, by simple insertion and inspection, 
the humid condition of the earth between the extremes of perfect 
dryness and of aqueous saturation, as the thermometer discloses 
heat of temperature, we should indeed become possessed of two 
ready and sufficient means of quickly ascertaining the principal 
phenomena on which the temperature of soils depends ; we should 
be provided with tests, which would go far towards explaining 
certain causes and degrees of fertility, and possibly find ourselves 
armed with an expeditious method of deciding on the aids which 
a given soil might require for increasing its fructifying properties 
and power. The mention of a desideiatum is occasionally half 
way towards its fulfilment; and we may hope that the resources 
of science will avail for the supply of an instrument which would 
be so precious to the enlightened agriculturist. 
Thus far had I written last year, as you are aware, and deemed 
my task terminated. Having had, however, the good fortune to 
obtain a record of observations illustrating, very forcibly, the ne- 
cessity of draining retentive soils — by bringing within the scope 
of arithmetical computation the quantity of rain-water which is 
annually evaporated from the mass of the soil, "at depths acces- 
sible to the cultivator," and the quantity which either permeates 
porous or must stagnate in retentive soils — I have appended the 
following section to the foregoing discussion, as contributing to 
establish certain statistics of drainage, or, to use your own remark, 
" as striking a debtor and creditor account between the earth and 
the sky.'' 
On the Quantity of Rain compared , ivith the Quantity of Water 
evaporated from or filtered through Soil ; with some Remarks 
on Drainaye. 
Wi<; are indebted to Mr. John Dickinson of Abbot's Hill, near 
King's Langlcy, Herts (the eminent paper-manufacturer), for a 
register, extending over the period of tlie last eight years, of the 
quantity of rain which has fallen in his locality, and of the quan- 
tity which may be presumed to have passed through the soil. 
The first datum is determined by the common rain-gauge ; the 
second is derived from a gauge invented many years since, for this 
special purpose, by the illustrious ])r. Daltcm. And herebv we 
obtain, very uncxjiectedly, as regards botii the facts and the ex- 
tensive range of observations, experimental illustrations of the 
desiderata numbered [•> and 0 (page 18). The c(mstruction of the 
rain-gauge needs no remark, and the Dalton gauge is equally 
