January i, i8qi.] 
THE TROPICAL AQRICULTURtST. 4^9 
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I should have misapprehended or misstated its 
effect, I quote the paragraph from Professor Unwin’s 
paper :— “ The term water-power is convenient but 
inaccurate. Strictly speaking there is no such 
thing as water power. Whether the water des- 
cends on a water-wheel, or actuates a pressure 
engine in connection with Mr. Ellington’s 
pressure mains, the water is a mere agent of 
transmission. In the one ease the water-wheel 
is driven by the energy of gravitation, in the 
other by the energy developed in a steam 
engine ; the water merely transmits the. pull of 
gravity, or the push of the steam engine. In neither 
case is the water itself the source of the power 
utilized. As we speak of a steam engine as a heat- 
motor, so we might speak of most water-motors as 
gravity-motors,” Another principle is thus stated : — • 
“ The ordinary source of water-power is a supply 
of water raised by the sun’s heat to a convenient 
elevation, and falling through natural channels back 
to the sea,” and then follow mathematiral proofs. 
It is fortunate for us in Ceylon, that, in the absence 
of coal and the increasing scarcity of wood fuel in 
convenient situations, water thus returning to the 
B(a is so generally present in a form easy of 
utilization, especially in our hill regions. Professor 
Unwin states even of Britain, that ‘‘ No great 
increase of the price of coa' is needed to make water 
power of much more value than at present. On 
the other hand if the electrical engineer will make 
the transmission of energy easier, the importance of 
water-power would also increase, for one of its 
greatest defects is that it exists in the localities 
where nature has placed it, and not in the piaops 
where it can be most conveniently used.” Tho 
author believes that the electrical transmission of 
water-power would be common, if a diminution of 
tho cost of eleoirieal apparatus took place. On the 
Continent of Europe and especially in America, 
water-power is very largely utilized, and at Holyoke, 
below the rapids of the Connecticut river, water 
power is supplied to mills at the rate of 20 shillings 
per horse-power, per annum,— the cheapest manu- 
facturing power in the world. While I believe in 
ffood turbines where considerable power is required, 
and skill and intelligence are readily available, wa 
have always had much faith in the common and 
simple overshot-wheel for ordinary purposes. Two 
such wheels, equal (o 8 or 9 hotse-power are 
sufficient for most tea factories. I again quote 
Professor Unwin ; — " By a bucket water-wheel we 
can recover the energy corresponding to an un- 
expended part of the fall ; by a pressure engine we 
can get the energy due to the pressure, and by a 
turbine we can get the energy due to the velocity. 
First then there are bucket or oell wheels, in which 
the water fills the buckets near the lop of the fall 
and descends in contact with the wheel without 
acceleration. About this class of motors I have 
time to say very little. They are simple in prin- 
ciple and have a taiily high efficiency. But they 
are somewhat cumbrous and antiquated machines. 
On falls above 70 feet they cannot be used. On 
fulls of 20 to CO feet a turbine is cheaper, and 
yields an equal efficiency. [Does the world 
‘ cheaper ’ apply in Ceylon ?] On a low fall, if 
a turbine co.ts as much, it has, if well constructed, 
a higher effioicncy. Still, in one respect a good 
overshot or high breast wheel is superior to most 
modern water motors. Its eficieunj is nearly 
the same with a reduced sujyply of water as ivith 
the full sujijiiy. lu this respect many turbines, 
oiherwiso excel! nt, compare very unfavourably 
with the water-wheel.’ Compared with steam, 
water is 500 times heavier, and its incompressi- 
bility and inertia arc disadvantages. Of an under- 
shot wheel it is remarked, that apart from the 
losses by the friction and leakage, it utilized less 
than half the energy of the fall. The Professor 
does not believe in more than 80 per cent 
efficiency in turbines and does not regard the 
American turbines as better than the British. 
The description of the various classes of turbines 
sounds like scientifio gibberish: — ‘‘There are, there- 
fore, outward flow, inward flow, and axial or 
parallel flow turbines.” But Professor Unwin 
looks on the hope of turbines with greater normal 
efficiency then 80 per cent as equivalent to the 
search for the philosopher’s stone. — I have noticed 
Professor Unwin’s paper first because of the im- 
pression made on me by his denial of the existence 
of innate power in water, but the first of the series 
is a veiy able paper, by Mr. John Evans on 
Physiography, in which the laws of our atmosphere 
are analyzed in the spirit of that wonderful 
passage in the sacred record ; — ” All the rivers 
run into the sea, yet the sea is not lull ; unto 
the place whence the rivers come, thither they 
return again.” Beyond this alternative movement 
of moisture from the sea via the atmosphere to the 
hills and thence back to the sea science has not 
progressed. Practically tho atmosphere is never 
free of moisture, but neither diffused moisture 
nor steam is visible until condensed by cold 
into small particles of water. ‘‘ The quantity of 
moisture present in the air varies considerably in 
diflerent countries and at different seasons. Here 
in England it is said that the average proportion 
of water present in the air is about per cent; 
When the air at an ordinary temperature is 
nearly saturated, a slight reduction of heat euffioes 
to make the moisture visible. How often do 
we not see a mist rising, as it is called, 
towards sunset, after a bright, warm day ; 
and how often have we not seen the morning’s 
mist, and even the olouds at a higher level, gradu- 
ally disappear under the genial influence of the 
sun’s rays.” Evaporation is often almost equivalent 
to rainfall. At Madras it has amounted to 90 per 
cent annually ; and the hot winds of the equatorial 
regions get surcharged with moisture, which they 
deposit mainly at 4,500 feet altitude on mountain 
sides in India, and Ceylon, the level of greatest 
deposit in England being at 1,500 feet. ‘‘Mountain 
ranges indeed are the great condensers of atmos- 
pheric moisture, and the amount of rainfall in 
any country is in the main dependent on the 
position of these ranges, and the prevailing direction 
of the winds.” Whatever local effects forests may 
have, in modifying climate and preventing floods, 
my experience is that it neither increases nor 
diminishes rain, where warm clouds come laden 
with moisture and there are mountains, no matter 
how bare, to condense the moisture, “ At Seth- 
waite in Cumberland, the average rainfall is 140 
inches.*” At Hunstanton in Norfolk and else- 
where it is little more than 20 inches ; so that 
on an average there is seven times as much rain 
in one part of England as there is in another. 
In India the disparity is still greater, between 500 
to GOO inches at Cherapunji and 4 or less in 
p'aces in Sind. Some of your reiders may bo 
interested to learn that 1 foot of undrifted snow is 
the rough equivalent of one inch of rain. Tbero 
is much of interest about the capacity of different 
soils to absoib and retain moisture and about 
subterranean water and its temperature, ri.ing 1 deg. 
with every 50 feet or so of depth. ‘‘ It cannot 
be too often insisted that, in the case of water 
supply derived from porous soils, ills in the highest 
degree illusive to depend on averages. The mini- 
mum, or, at the beat, the lowest average of three 
* At Stye, iu CunibeiliiLd, in 1883, no less tbau 190 
iiclics fell 
