MAGAZINE OF SCIENCE AND ART. 
145 
sion of such a mass of information as will very much 
facilitate tlie application to other districts ot the prin¬ 
ciples upon which the proportion of the supply to waste 
has been now determined. 
Having shown that a sufficient supply ol water can 
be procured, the next matter tor consideration is the 
means by which it can he made available. The works 
which it ■will ho necessary to construct lbr the purpose 
of collecting, conveying, and distributing the watei\ are 
identical in principle with those to which 1 have before 
alluded. Dams will be required to collect the water, 
channels to convey it, and special arrangements will 
have to be made for its measurement and distribution ; 
blit as the supply will depend upon the casual fall of 
rain, the dams will have to bo small and numerous 
instead of tew and of largo dimensions; and as a neces ¬ 
sary consequence the channels from each reservoir will 
be of smaller dimensions than would be the caso where 
one large canal, drawing its supply from a river, con¬ 
veys all the water required for irrigation of an extensive 
district. 
In the country the water will be arrested at every 
convenient spot, and a portion of that which would 
otherwise run to waste will be kept hack in a reservoir 
as a source of supply during the dry season. 
This system won Id arrivo at its perfection when the 
whole of the flood water would he retained, and the 
streams brought under such command as to allow of 
the requisite supply being doled out through sluices to. 
meet the wants of the settlers on the banks. This, 
however, must of conrse be the result of centuries of 
work. I only allude to it at present as being the limit 
beyond which* it would be useless to go, but to which 
we ought to strive to attain. As regards the mode of 
construction of the different kinds of works a few 
general remarks are all that can properly find place in 
such a paper as this. In some place the dam may be a 
mere bank of earth or clay, raised sufficiently high to 
be beyond flood level, with culverts largo enough to 
carry off all the surplus water. In other places, the 
dam may be formed of rough blocks of stone, with an 
unstream facing of earth. Here timber may be used ; 
then timber and stone. In fact, the rule should be to 
make use of the material which Is most convenient, 
provided, of course, that it would form a substantial 
and permanent structure* Particular care should bo 
taken to guard against damage from floods. Generally 
speaking, it would be wiser to go to some extra expense 
in preparing a water channel for surplus water, than to 
allow the flood to rnsli over the dam itself; but in 
daces where a dam is erected in a water-course, which 
ias its head in mountainous ground, the floods come 
down so rapidly and heavily that no reasonable amount 
of waste channel would suffice to carry them off. A 
rise of 50 or GO feet has been known to take place in 
some of these streams in a few* hours. Under such cir¬ 
cumstances the oulv course to adopt is to make the dam 
of the best material, and to hind it together in such a 
manner as to secure it from damage, should the floods 
roll over it; and for such a purpose a mixture of timber 
aud stone will probably answer best. The framework 
of timber will serve to bind the whole structure to¬ 
gether, and the masses of stone will give the necessary 
weight and stability. 
It would he very desirable that, wherever a road is 
made to, cross a valley or a ravine, a dam should he 
formed instead of a bridge. In many cases a simple 
culvert would be enough to carry oft’ the surplus water, 
and a permanent pond -would be created, varying in 
size according to the slope of the ground. In other 
places the discharge would bo so great at times as to 
require the whole length of the dam as a waste weir, in 
which case the road w'ould have to bo raised above flood 
level, in order to keep it always open as a means of 
communication. 
When the porous character of the soil compels the 
settler to have recourse to wells, the mode of raising 
the water from these wells will, of course, require a 
good deal of consideration. Windmills, steam engines, 
horse or animal powetq may all bo applied, and the pre¬ 
ference to be given to one kind of power over another 
will depend upon their relative economy. The follow¬ 
ing considerations may serve as a guide to the settler 
in prosecuting his investigations :— 
In the first place, the quantity of water which a well 
can furnish should be ascertained, and tills, of course, 
will determine the amount of the power -which it will 
be necessary to employ. An engine of one liorse-power 
will raise 33,000 lbs. one foot high in a minute, and as 
water weighs 03 5 lbs. per cubic foot, a horse-power is 
equivalent to 528 cubic feet of water raised 1 loot high, 
in a minute, or 8’8 cubic feet 1 foot high in a second, 
or '176 of a foot 50 feet high in a second. Now 1 cube 
foot of water per secoud will irrigate 100 acres of laud ; 
•17G of a cube foot, will, therefore, irrigate 17*6 acres. 
So that the power of a horse applied to raise water from 
a depth, or to a height of 50 feet, will be sufficient to 
irrigate 17‘G acres ofland. 
It would, as I have said before, be out of place in a 
paper of this kind to enter into detailed descriptions of 
the works to be constructed. I trust, however, upon 
some future occasion, to be able to bring before the So¬ 
ciety accounts of the works which have been erected in 
India. I have written both to Calcutta aud Madras for 
fall information as to these works. Such an account 
will form a valuable supplement to tliis paper. At 
present I have limited myself to a sketch of tuo value 
of the work when completed. I hope hereafter to bo 
able to explain how the work should bo done. 
Although it would be impossible to give even an ap¬ 
proximate estimate of the cost of the works to which 1 
have alluded above, yet this paper would be obviously 
incomplete were T not to allude to those financial con¬ 
siderations which must always have a most important 
influence in determining the adoption or rejection of a 
scheme, the object of which is professedly the increase 
of the national wealth. The test, of course, by which, 
such undertakings must he tried is an arithmetical one, 
and the question to be asked is, Will the benefit expected 
to be derived from tho expenditure of any given amount 
of capital be sufficient to meet the cost of working aud 
maintenance, aud to return, in addition, a fair interest 
upon tho original capital? In replying to this ques¬ 
tion, we must be careful not to take too narrow a view 
of the benefits which are likely to result from works of 
what are called public utility. The indirect returns 
must be taken into consideration, as well as those which 
are direct and obvious. In a paper which I read some 
time ago to the Society I laid great stress upon the di¬ 
vision of the returns from the railroads into direct and 
indirect, aud showed that the proceeds nnder the latter 
head were of far greater importance^ than those under 
the former. The observations made in that paper will 
apply in principle to the returns from works constructed 
for irrigation. In a former part of this paper I have 
given an instance on which, while tho direct return de¬ 
rived from the rent of tho water did not exceed four per 
cent., tlie indirect return—that is, the benefit to the 
person who made use of the water, to irrigate his pro¬ 
perty, amounted to upwards of 30 per cent, upon the 
capital expended ; it is evident, therefore, that the 
benefits to the community which are represented by the 
total return from the undertaking, might be very great, 
though the persons engaged in it, be they individuals, 
or a Company, or the Government,—should obtain no 
interest at all upon the capital laid'out. Again, in 
estimating the returns, either direct or indirect, from 
money expended in railroads, canals, or works of irri¬ 
gation. wo must be content, in many instances, to look 
upon them in the light of a deferred annuity ; that is, 
we must he content with a less present interest upon 
the outlay, in consideration of the greatly enhanced re- 
tumes in future years. 
As good an instance as I can bring forward in illus¬ 
tration of my meaning, will be the New River water¬ 
works by which water is brought from certain springs 
in Hertfordshire, and from the river Lea, for the supply 
of London, The work was undertaken by Sir Hugh 
