MAGAZINE OF SCIENCE AND ART. 
cultivation. The action of the atmosphere, and the 
passage of the water over a sand or pebbly bed, appear 
to combine in purifying and rendering it more fit for 
the use of man. 
The next source from which water is frequently 
obtained, whore rivers are not available, is from springs, 
wells, or artesian borings, driven into the water-beating 
strata which may underlie tliu surface of the ground; 
but tbe waters obtained in tins way, although frequently 
sparkling and clear, almost always contain chemical 
salts in solution, differing, of course, in quantity and 
kind with the geological formation of the country, avd 
the constituents of its soils; but water is rarely got by 
artesian borings in any but tbc tertiary formation, as 
in the earlier formations the absence of those clay or 
chalk basins with their alternating beds of clay, gravel, 
and sand, into which the water percolates, and in which 
it is retained, renders it useless to attempt to procure | 
it; and even in the secondary and transition series the 
water obtained from this source is seldom abundant or ] 
of good quality. 
The third means of obtaining a supply of water is one 
to which recourse must be had where neither of the other 
sources arc available,—it consists l« storing the surplus 
rain water which falls during the wet seasons, and 
holding it In reservoirs artificially constructed for rhe pur¬ 
pose. There are but very few parts of tbe earth where 
water sufficient for the use of man does nut fall annually 
in the shape of rain—and, consequently, there are very 
few places where water may not be had in sufficient 
quantity by adopting the commonest precautions for re¬ 
taining it. Very many places may be instanced in which 
the inhabitants are entirely dependent on the rains for the 
necessary supply of water. And l am induced to think 
that it is the principal source from which we must look for 
a supply for the wants of this country. Any person who 
has seen much of the interior of New South Wales cannot 
but have been struck with the scarcity and utter insigni¬ 
ficance of the running streams, and we hare all heard of 
the fearful los*et of stock, which have oceured during 
those seasons ■ f drought to which this country dike many 
others under the same parallels of latitude) is occasion¬ 
ally subject. 
I allude more particularly to the middle districts of New 
South Wales, for to the northward of the tropic, within the 
zones of the tropical rains, water appears to be more 
abundant; it appears to me, therefore, that every en 
couragement should he given for the formation of dams 
for the storing of water In all situations where they are 
practicable. 
The inhabitants of Parramatta having long felt the 
want of a permanent supply of good and wholesome water, 
h3d, after a careful analysis of the wafers of Parramatta 
River and its various tributaries, at length finally decided 
in favor of Hunt's Creek, a branch running into the river 
on the north side, about three quarters of a mile above the 
town. The country drained by the creek Is a rugged 
sandstone tract of ahont 2100 acres in extent ; being 
unfit for agriculture, there is little or no risk of tU 
waters becoming tainted by the decomposition of animal 
or vegetable matters which might be used for manure, or 
by the mud brought down by the rains, should it ever be 
brought under cultivation. In this particular it differed 
from the Parramatta River and its other tributaries, all 
of which drain basins, either now under cultivation or 
capable of being brought so, and whose waters might con¬ 
sequently be subject to the objection before alluded to. 
A subsequent analysis of the waters of Hunt’s Creek and 
of the Parramatta River by Professor Smith, of the Syd¬ 
ney University, has fully established the fact of the superi¬ 
ority of the former, and I trust it will not be considered 
out of place if I avail myself of this opportunity of ex¬ 
pressing my thanks to Professor Smith for the politeness 
with which he furnished me with copies of his analysis, as 
well as much other valuable information on the subject of 
these waters. 
At the spot where the dam wall has been constructed 
two projecting masses of sandstone contract the valley to a 
width of about 220 feet, above this it expands into a wide 
basin extending for about a mile up the creek. The wall 
iso! feet in height from the centre of the culvert through 
which the mains will pass, to the coping, and about 12 feet 
from the bottom of the foundation course to the centre. 
The thickness of the wall at the base is 15 feet, tapering to 
7 feet 6 inches at top. It is built in tbc form of an arch 
of 160 feet radius. All the masonry in the wall is of the 
best ashlar throughout in two feet courses, set in Roman 
cement, the stones having all been carefully dressed to 
templates, so that all the vertical joints have been made 
to radiate truly to the centre of curvature; in the lower 
courses of the wall, where every succeeding course greatly 
lengthened the span of the arch, as will be seen by the 
accompanying sketch, and where on that account there 
might be some inequality in their resisting powers, l had 
the stones notched down one inch on the bods so as the 
better to resist any tetnlaney to slide. This may have 
been perhaps almost unnecessary, and the section of the 
wall shows it to be sufficiently strong to resist the pressure 
of the water (which will amount to about 2019 tons) in¬ 
dependently of its arched form, from which of course it 
derives its principal strength), but llion l have always been 
of opinion that when dealing with water, an engineer can¬ 
not be too careful to lmvc an access of strength in all works 
intended to resist its pressure. Ami I thought it would 
be well to have the power of increasing the capacity of the 
reservoir (which may easily be done by adding a few feet 
to the height of the wall) should the requirements of 
Parramatta ever demand it. When complete the wall 
will contain about 76,930 cubic feet of jk* 80 nry; and 
the entire cost of the work will amount to about £1.5,000. 
The quantity of water which tbe reservoir above the Dam 
will be capable of storing, may be estimated at 105,726.700 
gallons. The inhabitants of Parramatta, according to the 
last census r. turns, amounted to 5,129, and if we allow 
2 1 gallons per day for each person, and say as much more 
for cattle, ^manufactories, and waste, we may estimate 
that the daily consumption will amount to 217,160 gallons, 
and that the annual consumption will be 79,263*400 gal¬ 
lons Fo that the reservoir being once filled will contain 
183 days water. In this estimate I have neglected the 
evaporation, theamount of which it is difficulttn calculate; 
but, as there is a permanently running stream (though a 
small one), and a certainty of the reservoir being filled 
several times during the year (as I shall presently show)* 
it may I think be omitted. 
The rain gauge kept at the South Head shows that the 
mean annual fall of rain duriug the twelve years from 
tS40 to 1852, amounted to 4io3 inches, and the least 
quantity which fell during that time was 21 13 Inches, 
which occured during the dry year of 1849. These 
measurements having been made close to the sea coast, some 
deduction—-one-third say—must be made for the inland 
situation of Parramatta. 
This will lease 11 inches as the probable fall near Par¬ 
ramatta in the driest year which we have had since 1810; 
and if of this 14 Inches we allow one half for evaporation 
I and waste, we may, l think, safely estimate that the re¬ 
maining 7 inches would drain down into the reservoir ; 
this multiplied by the area of the basin, cqual.to 2100 
acres, gives 320,166,000 gallons, or over six times the 
consumption during years of the greatest scarcity; in 
ordinary times it would exceed twelve times the greatest 
demand. 
In order in some degTee to purify the water before its 
distribution, I propose constructing a filter round the 
mouth of the pipe, through which it will be drawn off from 
the reservoir. 
This 1 Intend to effect by enclosing the end of the main 
in an oblong brick tunnel, the top and sides of which will 
set in cement, so as to prevent the water passing through 
them, but in the lower course, open spaces will be left at 
stated intervals for its admission. Then, by covering the 
ground around the outside of the tunnel with a filtering 
bed, 5 or 6 feet in thickness, composed of alternate layers 
of broken stone, gravel, sand, and charcoal, through which 
the water will have to desceud before entering the tunuel, 
most of the lighter particles of organic and other matters 
will be deposited. The water will then have to pass 
through the openings in the side walls of the tunnel, and 
ascend through a filter inside of it, composed of similar 
