148 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 
and irrigate large areas, great engineering knowledge is necessary^, 
although there are no principles contained in hydromechanics that are 
not common to all times and places. 
But the more immediate object of these remarks is to draw attention 
to the great value of saving and using the rain falling on vineyards^ 
nurseries, market gardens, and farms, especially in relation to the cases 
where the whole of the rainfall can be saved from roofs. The first 
thing to awaken interest in the subject is to consider what really the 
amount of water the rain of twelve months means. 
Every one can easily obtain the information, which is practically 
mathematical, belonging to his own surroundings. Then arithmetic will- 
astonish him. Taking as example an acre of land, and finding the 
average rainfall upon it, multiply the average in inches by 22,623, and that 
will give him the annual quantity of water falling upon that acre in gallons, . 
or multiplying the inches by 101 will give the tons per acre. In the • 
North of London there are meteorological stations, among others, at 
Finchley and Muswell Hill. The former station is conducted with great 
care by Mr. J. W. Scott, who has kindly helped me with his experience 
and accurate data. Mr. Scott has demonstrated that in the district 
named there is a remarkable deficiency of rainfall in the last fourteen 
years, as shown by a decrease in the annual average of 1'89 inches as com- 
pared with the twenty-eight years' average, equivalent to nearly 7 per 
cent. It is most important, in judging for practical purposes the annual 
rainfall of a district, to prevent over-estimate, that the true average should 
be used for calculation and not any individual year's result. In the North 
of London the average rainfall from 1886 to 1899 inclusive was 25*56 
inches at Muswell Hill, and 25*35 inches at Finchley. So that at 
Finchley, leaving out decimals, 573,493 gallons, or over 2,500 tons of 
water, falls annually upon each acre. In parts of the district an equiva- 
lent quantity costs over £28. These are facts that require arranging tO' 
get at practical results. 
If an acre of land is an open farm or garden, then of course the pro- 
portion that can be saved depends upon the texture of the soil, the 
contour of the land, and the manner of drainage. The results recorded, by 
the late revered Sir J. B. Lawes and Sir J. H. Gilbert with regard to the 
percolation of the rain at Rothamsted from 1870 to 1899 are very 
valuable in that they afford us information as to the amount of rainfall 
that passes into what are called the springs. It has been proved at 
Rothamsted that in the winter months more than one half of the rain 
penetrates into the soil, and is available for the springs ; Vv4iile in summer 
only about one quarter passes down to the underground storage. So ■ 
that, taking the whole country over, it may be said that, assuming the 
soil and subsoil at Rothamsted to be of such a medium character that in 
some parts of the country it is more retentive and in some less, it follows 
that the proportion of rain stored by percolation is less than half what falls.. 
The more highly cultivated a country is, the more quickly the rain 
passes into the drainage, and the belief that the great watersheds of the 
country are lower than formerly, and are less plenished in modern days,, 
together with the greater strain upon the underground supplies by the- 
pumping for domestic and other purposes, throws into greater import-- 
