278 
THE TROPICAL AGRICULTURIST. [October t, 1889. 
off after a first irrigation, and wbat further area it 
can usefully irrigate before being finally discharged 
or absorbed. 
That the irrigating duty of this surplus is often 
very great in this country is shown by the great 
differences that exist between the areas irrigated per 
square mile of drainage basin of purely rain-fed tauks 
which are situated close together, and subject there- 
fore to the same yearly rainfall. The areas irrigated 
per square mile vary from 20 to 100 acres. Some 
part of this great difference may be explained by 
the fact that the larger and the deeper the tank the 
greater will be the area per square mile of drainage 
basin proportionately irrigated under it, but probably 
much of the difference is due to the greater use made 
in some cases than in others, of surplus water 
flowing off fields after first and second irrigations for 
watering fields on a lower level. In Tanjore, the 
lower we go down in the Delta the less is the out- 
turn per acre of cultivation. It would be interesting 
to ascertain how much of this is due to the poorer 
soils found towards the coast, and how much to the 
fact that the water supplied has been already used 
in irrigation in the higher parts of the Delta, and 
is therefore less rich in nutritive qualities. It is 
known for instance that water charged with carbonic 
acid — as water always is when it has been used once 
or twice in irrigation — does not part so readily as 
unusfd water, with the nitrogen held in solution. 
All this goes to support the opinion already expressed 
that the question to be solved is one for the agri- 
cultural chemist rather than for the engineer, unless 
indeed the later happens also to be a qualified chemist, 
a combination not likely to be found. Experiments 
have erred in making no distinction between the 
methods of irrigation adopted in this country. In one 
method the field is submerged, that is, a basin is 
formed, and the water, to a depth of 3 to 6 inches, 
is impounded therein, and only renewed when it has 
been nearly absorbed and evaporated. In another a 
continuous stream of water is kept up, and the plant 
continually comes into contact with fresh supplies of 
water, and therefore finds more food to assimilate. 
It has been found in France that the former method 
only requires one-fifteenth of the water required in 
the second. Although this proportion, on account of 
the greater evaporation, would not be so great in 
India, yet the forced adoption of the method of sub- 
mersion in times of scarcity and in bad years might 
lead to the saving of large areas of valuable crops at 
critical periods. Another point which has not received 
proper attention is the degree of permeability of soils 
experimented on. The more permeable the soil, the 
greater the consumption of water. In the Vosges 
wherd the supply of water provided for the irrigated 
areas is always great in granitic soils, which are of a 
very absorbent nature as much as 102 cubic yards 
per hour per acre are consumed, whilst for non-ab- 
sorbent soils the supply falls to 40 cubic yards. 
The solution of the question then which we set 
out by asking is one of the utmost importance to the 
engineer who has to design and carry out works of 
storage and distribution to the land owner and 
cultivator whose interest it is to get out of the land 
without exhausting it as much as it will produce ; 
and, on grounds of health to all those who have to 
live near or surrounded by rice fields. Nadult de 
Buffon in his valuable work on the Italian irrigation 
system citf-s two eases tending so shew that when 
the water supply is abundant and sufficient rice 
fields cease to throw off miasma, and therefore to 
affect injuriously the health of those living iu their 
neighbourhood. We cite one only of these cases. In 
Java before the construction of the dam across the 
Pooran^', near the town of Somabaga the supply to 
the surface irrigated was not more than 40S cubie 
yards per hour per aore ; fever and malaria were 
then prevalent. But immediately the volume of water 
wns increasi d by the action of the dam to 6'12 cubio 
yams, all sickness disappeared, It will be observed 
that these quantities are greater than are supposed 
to be required in India. The Government, then, would 
do well to undertake the kind of experiments necessary 
to solve the question we have raised, exhaustively 
and conclusively. We have only been able to indicate 
a few of the omissions of the past, but we have 
said enough to shew that further experiments are 
highly desirable. Before the experiments are com- 
menced, rules for the guidance 0 f those in charge 
of them should be carefully drawn up, both to pre- 
vent the repitition of mistakes, and to aliow of practical 
deductions being made from facts that may be es- 
tablished. The record of experiments made by French 
and Italian Engineers might be usefully taken as a 
guide to the way in which such experiments should 
be conducted.— Madras Mail. 
♦■ 
CEDAE PENCILS. 
The manufacture of Red Oedar pencil-wood has for 
years been almost exclusively confined to Florida, where 
this tree (Juniperus Virginiana), grows to a large size 
and in great perfection. The business has been in 
the hands of a large foreign house, which supplies a 
good part of the world with lead-pencils, and has been 
profitable. Large Cedar timber, straight grained, 
and of a suitable quality for pencil-stuff, has become 
scarce in Florida along the streams on the west coast, 
where the best was found ; and factories are spring- 
ing up in different parts of the south, especially in 
Alabama, where, at Gurley, sawing pencil-stuff is 
already a considerable industry. The best Red Cedar, 
however, now left will be found near the Red Elver, 
in Texas, and in the Indian Territory, where this tree 
attains a greater size than it reaches in Florida, 
while the quality of the lumber is not, probably, in 
any way inferior. 
The world has become so accustomed to using 
pencils made of Red Cedar, that it will not readily 
adapt itself to any others. The supply of this lum- 
ber of suitable quality, however, is not large in pro- 
portion to the demand, and cannot hold out many 
years longer. 
The Red Cedar is the most widely distributed of 
North American Conifers, and in some parts of the 
country it is one of the most common trees ; but it 
is in a few favoured localities only that it grows in 
a way to produce the straight-grained material essen- 
tial for pencil-making. 
The distillation of oil of Cedar, for which there is 
now a large commercial demand, from the sawdust 
and other refuse, has been profitable in the pencil- 
mills at Cedar Keys in Florida, and might be carried 
on to advantage in other parts of the cou ntry. It 
can be made, of course, from wood of the poorest 
quality. — Garden and Forest. 
TEA AND OTHER MACHINERY. 
The Blackstone Roller.— Facts are very stubborn 
things, and those to which Messrs. W. H. Davies call 
our attention in their important letter in another column 
afford irrefragable proof of the capability of the ' Black- 
stone' roller. We are particularly glad to see this 
testimony, because we heard quite lately of a case in 
which the machine was complained of. As we have 
had a good deal of experience of machinery of many kinds 
we have found that machines are themselves some- 
times very stubborn things. 
We call to mind the case in our own experience of 
a huge machine which was supplied to an eminent 
engineering firm who, after prolonged trial, declared 
it to be a failure. As it had already been fully tested 
before it left the manufactory, it was certain that the 
fault was in the treatment it had been subjected to. 
Therefore a foreman was sent from the factory to see 
what was the matter. Before attempting to work 
the machine, the emissary examined it carefully, and 
found that it was very slightly off the levol. Adjust- 
ing it carefully iu this respect, and having satisfied 
himself that it was otherwise in order, he set it to 
work and proved it to be altogether perfectly satis- 
factory both to himself and to the purchasers. The 
fault was not in the machine, nor in its construction, 
