Letters: Water from the air
In regard to your features series ‘Making Water Work’ (beginning 23
March): although it may not be practicable to pipe fresh water to desert
areas, it may be possible to obtain it from an abundant source often forgotten
by the thirsty dwellers of those regions – the atmosphere. Desert air may
be low in relative humidity because of its high temperature, but it will
contain water vapour, which could be condensed onto a cold surface into
liquid water. The question is, could such a process be made economical?
In the Namib desert, beetles stand on sand dunes to catch the night
mists and drink the condensing water. The dew point is reached at, let us
say, about 10 掳C. At this temperature, air contains 1 kg of water per
106.4 cubic metres, and it will contain about the same mass when heated
to the normal day temperatures of 45 掳C. To precipitate this mass, we
must chill the air to 10 掳C. Much of this heat extraction could be achieved
by passing the air through heat exchangers buried underground. The greatest
energy requirement is to remove the latent heat of vaporisation of water,
which is 226 x 104 Joules per kilogram. This is only 0.628 kilowatt-hours,
and could be provided from a solar array. A 5-square-metre array of silicon
cells should generate around 0.75 kilowatts, which over a 10-hour daylight
cycle should produce about 12 kilograms of deliciously cold and very pure
water.
Colin Cook Basildon, Essex
Letters: . . . and the sea
In ‘Fresh water from the sea’ (31 August), you described various methods
of obtaining drinking water from the sea. The techniques you pictured included
various methods of evaporative distillation, and the use of high pressure
reverse osmosis.
Quite a few years ago, I came across yet another method being used,
namely fractionation via freezing. As the sea water was frozen, the ice
produced tended to be composed of fresher, drinkable water.
Danny Burstein Flushing, New York
Letters: . . . and the rain
I am prompted to write by your report of the problems facing suppliers
and consumers of water in Britain (Forum, 7 September).
Whilst the imposition of meters will reduce demand by making people
aware of the cost of water, there is a more radical approach which has yet
to be seriously explored. That is, the provision in every new building of
a cistern or cisterns to store rainwater, of sufficient capacity to provide
at least one week’s normal supply for toilet flushing and other non-drinking
uses such as cleaning. The cisterns would be the normal source of supply
for these services, the mains supply only being required after dry periods
when cisterns became exhausted.
It seems to me that to supply expensive, clean, potable water for any
and all uses for which the consumer cares to employ it is fundamentally
unsound. As with so many of our modern problems, the solution does not lie
in vast expenditure on reservoirs and national water grids, but in old,
small scale solutions to the same problems faced by our forefathers.
John Neimer Weymouth, Dorset
Letters: Shining intellect
In your leader (Comment, 21 September), you suggest that Mrs Thatcher’s
frequent reference to Faraday’s success as a scientist despite his lack
of formal university education smacks of anti-intellectualism. I’m quite
happy that Mrs Thatcher was the best qualified prime minister (in academic
terms) in the history of that post. Are you?
J. L. A. Hartley London
Letters: Big yawn
A recent popular TV science programme here featured ‘yawning’. It revealed
that it had been found that aeration of the lungs was not a function of
yawning. No reason for yawning has yet been established.
The function of yawning has been clear to me for 30 years due to observations
that I made while engaged in skin diving. During descent and ascent, the
air in the facemask and in the sinuses must be equalised to the ambient
pressure as it changes with depth. If this is not done, pain can be severe,
blood vessels can haemorrhage and the eardrums can rupture. Some divers
have no difficulty as the sinus ducts are clear and unblocked, but others
must hold their noses and blow or swallow or yawn. The action of yawning
involves the activation of muscles around the sinuses and their ducts so
that the ducts are opened up to allow air to pass through more easily. One
only has to initiate a yawn to experience the feel and sound of the muscle
action and the ears clicking as the air flows through.
My hypothesis is that yawning has the function of equalising sinus pressure
to ambient pressure and that it is initiated by inequality brought on by
atmospheric pressure changes. As people in a group are affected by the
same pressure changes, those affected by a build-up of pressure inequality
will tend to yawn at about the same time.
The boredom-and-yawning syndrome might be explained by the possible
effect of inactivity allowing the sinus ducts to become sluggish and blocked.
Divers have most difficulty with equalisation while descending; when
ascending, the air seems to escape from the sinuses without any conscious
effort. So it is likely that yawning might be most common during rising
atmospheric pressure.
I have found that I can sometimes ease sinus headache, the one behind
the eyes, by forced yawning or by holding my nose and blowing or sucking
according to whether the weather report shows the atmospheric pressure to
be rising or falling.
B. Marsh Huntingdale West Australia
Letters: Too late
I was interested and concerned to read of the problems in Sariska Tiger
Reserve (This Week, 28 September) but surprised that the picture caption
suggested that one of the animals in danger is the cheetah. There are no
cheetahs in Sariska Reserve – the species is long extinct in India.
Caroline Ross University of Durham
Letters: A meal of it
Perhaps mice do not eat white sugar (Letters, 5 October). So what? Neither
do humans normally ‘make up a meal’ by eating white sugar on its own directly
out of a sugar bowl. Sugar is normally used to make sour or unpalatable
foods more edible. Action and Information on Sugar and their friends might
like to add to their stores of knowledge that hummingbirds avoid saccharin
if given a choice between that synthetic sweetener and pure white sugar.
So what, you may well ask? Exactly. Hummingbirds, mice and Action and Information
on Sugars are about as relevant to nutritional science as this letter.
A. J. Vlitos World Sugar Research Organisation Reading
Letters: Flick it and see
I refer to Ian Anderson’s ‘Mystery bubbles’ (Letters, 5 October). The
pupils here at Clifton College Preparatory School have been observing this
effect while consuming their orange juice from plastic cups. Simply wait
until the cup is two-thirds to one-half full and then flick it, whereupon
the desired effect will be observed. Best results are obtained with the
hard transparent plastic kind of cup. The soft, white, granular poly-styrene
cup does not work.
Any explanation of this phenomenon will be gratefully received.
Robert Muston Clifton College Preparatory School Bristol
Letters: The Fractal and Firkin
Not long ago, over a casual pint, a colleague and I were bemoaning the
fact that scientific nomenclature is poorly represented amongst pub names.
To redress what we consider to be a serious imbalance, we compiled the following
list, drawn from all branches of science, for consideration by the breweries:
The Double Helix; The Hardhat and Hammer; The Charming Quark; The Visible
Spectrum; The Voltage Gate; The Neurotic Rat; The Magma Chamber; The Rod
and Cone; The Citation; The Abstract Chemical.
We would like to know if your readers can think of additions to the
above list and if they are aware of any more enlightened pubs in Britain
which already have scientific names.
Kimberly Martin Harlow, Essex
Letters: Corrections
In the Forum article ‘Getting to grips with left-handed yoghurt’ by
David Hall (7 September), an editorial error altered the setting of d and
l (in the d and l isomers of lactic acid) from small capitals to lower case,
thereby confusing molecular configuration with the rotation of polarised
light.
In ‘Casualties of Vietnam’s recovery’ (14 September), it was stated
that 200 000 hectares of forest are razed each year for export. In fact,
the majority of the wood taken from the forests is for domestic use.
Letters: The meat habit
Though it is difficult to be comprehensive about ‘What we must do to
save the planet’ (Talking Point, 7 September), one important change in behaviour
is not mentioned.
The potential benefits of reducing our meat intake never seem to get
the attention they deserve. For instance, meat production uses a lot more
land (involving deforestation) and water as compared to its dietary equivalent
in human feed crops. More and more studies point out that high intakes of
animal products are linked to diseases such as cancer and heart disease.
And, as a cover of the New 杏吧原创 pointed out a few years ago, cow flatulence
contributes to the greenhouse effect.
Shouldn’t the anti-ecological habit of eating meat therefore receive
a bit more attention?
Ariane Janer Rio de Janeiro Brazil
Letters: Dicey quote
I was delighted to read that Ariadne had chosen to write about the Oxford
Dictionary of Quotations (Ariadne, 21 September), but rather surprised by
her criticisms.
The quotation she notes as missing (Einstein’s remark that God does
not play dice) is in the third edition of the Oxford Dictionary of Quotations
published in 1979; and if she consults the Oxford Dictionary of Modern Quotations
published earlier this year she will find this quotation set in its longer
context, as well as a further selection of quotations from Einstein. This
is the appropriate place to look for twentieth-century quotations in general.
In this dictionary she will find a number of other modern scientists, including
Konrad Lorenz, Poincare, J. B. S. Haldane, Werner Heisenberg, Sir James
Jeans, Sir Julian Huxley, Ernest Rutherford and Bertrand Russell.
Sara Tulloch Oxford University Press Oxford
Letters: Netting dolphins
Recently Dr David Bellamy has been reported as saying that work on net
reflectors designed to warn dolphins of the presence of fishing nets was
‘the most promising piece of research yet to safeguard the mammals from
mass destruction’.
However, much research has shown that it is not the case that dolphins
and other cetaceans cannot detect the presence of nets. Gill nets made of
monofilament nylon 0.49 millimetres in diameter should be detectable by
bottlenose dolphins at distances of at least 5.5 metres, which should give
plenty of time for a dolphin to avoid them.
There are more complex factors to consider. For instance, dolphins do
not echolocate at all times and they are unlikely to expect to encounter
barriers in the open sea, or they may misidentify such an abnormal barrier
as a naturally occurring, non-damaging feature such as a kelp bed. They
may be attracted to the net because of the presence of fish and when concentrating
on the sonar reflection from the prey they are pursuing, may not detect
the net. Alternatively, the sonar reflections from fish entangled in the
net may obscure the net itself.
Efforts towards designing a net that is more visible seem unlikely to
succeed simply because this is not the underlying cause of dolphin entanglement
in fishing nets. While attempts are focused on doing that, dolphins will
continue to die. Such research also runs the risk of being used to legitimise
the continued use of large-scale drift nets. Not only are such nets completely
indiscriminate in terms of the species they catch, but they are also responsible
for dramatic overfishing of even the target species.
Susan Mayer Greenpeace London
Letters: Age gap
Although Kevin Woodcock (Letters, 5 October), ‘reminds’ us that Descartes
is reputed as being less than enthusiastic about Newtonian gravity, Descartes
had, in fact, remarkably little to say about Newton’s ideas on gravity or
indeed Newton’s ideas on anything else, something I’ve noted and remarked
upon on several occasions. After giving the matter some thought I’ve arrived
at the conclusion that this may be because Descartes died in 1650, when
Newton was eight years old.
I’m afraid it’s another case of putting Descartes before the horse sense.
Ralph Estling Ilminster Somerset
Letters: Dehorning rhinos
I was interested to read ‘Can we end rhino poaching?’ (5 October). As
your article states, Zimbabwe has just embarked on a dehorning programme,
following the example of Namibia. However, in Zimbabwe it is three white
rhino which have been dehorned in Hwange National Park, not black rhino
as in Namibia. Seven weeks after dehorning these rhino were exhibiting behaviour
more commonly associated with black rhino than white.
White rhino are grazers, found on open grassland in loose groupings
of up to seven or eight animals, and they are much less aggressive than
the notorious black rhino. However, the dehorned Hwange rhino have moved
into dense bush, away from their original group and have become aggressive
and unpredictable.
Many of the Park’s staff are urging caution in pursuing the dehorning
programme. Despite the success of the Namibian programme, the trauma of
dehorning may prove too great a price to pay to protect the white rhino
of Hwange.
Barbara Evans Cambridge
Letters: Research in peace
The report on Iraq’s biological weapons (This Week, 24 August) merits
a reply. Presumably the implication is that any research into even naturally
occurring anthrax, botulism and gas gangrene should be viewed with suspicion.
But should this really be the case?
People concerned with the prophylaxis, diagnosis and treatment of patients
suffering from or at risk of contracting such rare and exotic infections
have learned that all the natural conditions need to be satisfied before
many ‘disease producing organisms’ are likely to produce disease. Many scientists
(not doctors and nurses) have tried to misuse virulent microorganisms by
growing them artificially, making aerosols, loading them into ‘delivery
vehicles’, scattering spores and so on – but always with signal lack of
success.
When will the biological warriors finally come clean and admit that
biological warfare is not merely unethical and immoral, but is also practically,
strategically and financially unachievable? Surely now that the Berlin Wall
is down, the Iron Curtain is lifted and the Cold War is at an end, it would
be better for all governments to lift the veil of secrecy with which they
have clothed – in the name of security – the understanding of the molecular
biology of many acute and chronic infective conditions. Then perhaps one
of the peace dividends would be to allow free correspondence between those
in both developed and underdeveloped nations who are engaged in humanitarian
rather than military research (and we would include the medical personnel
of the Armed Services in this category) into the mode of action of microbial
pathogens.
M. and B. Corcos Beeston Nottingham