Letters: Swinging together
Q: Groups of greenfly on my honeysuckle often suddenly burst into rapid
synchronised side-to-side oscillations.
These bursts of activity last for 43 seconds, with an interval of 11
seconds rest before the next series of movements begins.
Individual groups of flies were separated by at least 20 centimetres
– some by up to 2 metres – but all groups on the plant were synchronised.
What were they doing and why, and how did they manage to ‘keep time’?
Douglas Cross Honiton, Devon
Letters: No panacea
In ‘Banana tree could feed hungry’ (This Week, 5 March), Rosie Mestel
reports that the enset plant (a relative of the banana that is indigenous
to Ethiopia) could help ward off famine. Citing the work of Steven Brandt
at the University of Florida, the article argues that it has been a ‘disastrous’
waste of money to invest ‘millions of dollars trying to build up cereal
production for this region’.
It should be pointed out, first, that famine and hunger are not just
about a lack of food; they result when poor people do not have sufficient
resources to gain access to food even when it is available on the market.
Increasing the production of a single crop will not in itself remove the
threat of famine. Raising incomes, improving health, building roads, removing
the threat of war and creating public institutions that can protect the
poor are all necessary to eradicate famine.
Second, enset is the staple food for only 15 per cent of Ethiopia’s
population. The other 85 per cent depend on cereals for almost 80 per cent
of their diet. Unfortunately, cereal production has been declining since
the 1960s at a rate of almost 4 kilograms per capita per year. This has
been due to inappropriate economic policies, population growth of 3 per
cent per year, high rates of soil erosion and numerous droughts. As a result,
raising cereal production and seeking ways to protect production levels
against climatic anomalies remain high priorities.
Third, enset is no panacea for hunger even in Ethiopia. It has a limited
growing environment, it is relatively light in calories, it is prone to
viruses for which no easy remedies are available, and its cultivation represents
a long-term investment rather than a solution to immediate hunger.
In sum, research on enset may indeed be valuable; but not at the expense
of research on cereals, pulses and livestock. Far from being ‘disastrous’,
investments by the US and other countries in increasing cereal output in
the Horn of Africa are essential to the long-term wellbeing of that region.
Patrick Webb and Stephen Vosti International Food Policy Research Institute
Washington, DC
Letters: Climb on the roof
It is with some glee that I read Joe Flower’s ‘There’s a starman waiting
in the sky . . .’ (19 March) about space-based utility, communication and
broadcast networks. As described, this technology works very well when you
are sunbathing on your yacht off Tierra del Fuego or filming the vast diversity
of wildlife in the Gobi; but where such truly marvellous technology will
be demanded most – inside modern, metallised, glazed and steel structures
or even the humble apartment block or hotel – your multimedia Total Electronic
Package, capable of communicating with one of billions of other TEPs and
receiving hundreds of television, audio and digital broadcasts, will be
about as useful as carrying half a house brick around in your pocket.
A little closer to earth I watch the blood drain from the faces of building
managers when discussing the cost of current Shared Antenna Television networks,
giving full access to just one popular broadcast satellite system. I wonder
who will foot the bill for some form of two-way Transparent Antenna Network
that will carry all those microwaves beating down uselessly on the roof
above to where they are needed: inside.
George Hayton Architectural Cable Services Kings Lynn, Norfolk
Letters: Ultrasound alert
Widespread antenatal ultrasound screening was introduced in Britain
despite lack of evidence of either its efficacy or safety (‘Screening without
meaning?’, 19 March). As a consumer group we started lobbying ministers
of health from 1981 onwards for adequate research. We have highlighted many
problems which have not yet been addressed.
Two studies have suggested an increased rate of miscarriage following
ultrasound scans, but the subject is inadequately researched. In 1992, a
randomised study of 2500 pregnant women receiving either two Doppler studies
of blood flow or not, found that four times as many scanned babies died.
This result is still unexplained. There are animal studies which have shown
‘delayed fetal lethality’ in scanned groups.
The Australian findings that insonated babies were smaller have been
repeated in many animal studies, including monkeys. Even more worrying are
the major behavioural changes in infant monkeys who had many scans in the
womb. A recent study from Northern Ireland has shown that 46 per cent of
pregnant women at one hospital had 5 or more scans, and 10 per cent had
10 or more.
Ultrasound equipment is getting more powerful, and the new vaginal probes
deliver greater ultrasound exposure to the fetus than most abdominal scans.
In many published research studies on fetal behaviour, babies have been
scanned for an hour or more.
With every female examined, we expose the ova for the next generation.
Beverley Beech and Jean Robinson Association for Improvements in the
Maternity Services Iver, Buckinghamshire
Letters: Lab safety
I am writing in response to Mick Hamer’s article ‘Lab blast rocks university
safety’ (This Week, 19 March).
King’s College, London, deeply regrets the accident which occurred on
23 February. The college has an excellent safety record with thousands of
students safely passing through the system. At this stage, while the Health
and Safety Executive, and the college, are conducting investigations, it
is not appropriate to anticipate the outcome of these investigations. Once
they have reported, it will be possible to ascertain whether procedures
need to be revised.
However, I would wish to make the following point: Hamer implies that
the procedures King’s employs differ from those which are used by the rest
of the university system. He states that King’s students are ‘supposed to
sign a form which spells out the objective of the experiment and the dangers
of chemicals involved’. This is not true. At King’s, as in most universities,
academic supervisors are responsible for risk assessments and for informing
students (undergraduate and postgraduate) of the hazards, risks and procedures.
King’s does not and would not seek to rely on the judgment of students
to ensure health and safety.
Furthermore, I would like to emphasise that King’s is not out of step
with usual university practice with regard to supervision. Nor are undergraduates
responsible for completing and signing Control of Substances Hazardous to
Health assessment forms.
Arthur Lucas King’s College, London
Letters: Sensible and safe
The amount of surplus weapons-grade plutonium in the world is certainly
a matter of great concern (‘A bomb waiting to explode’, 26 February). However,
Vincent Kiernan overlooks the obvious means of disposing of that plutonium
– burning it in fast reactors. Why are the Americans proposing to abandon
the only means of permanently disposing of plutonium? Why is Britain doing
the same thing?
Kiernan claims that the US military has ‘apparently’ exploded a nuclear
bomb constructed with reactor-grade plutonium. My information is that the
plutonium used for this test (in 1962) did not come from a reactor, civilian
or military, and that the US has never conducted a nuclear explosive test
which employed plutonium obtained from the reprocessing of reactor fuel
used in commercial nuclear power plants (in fact, US law prohibits such
use).
Consequently, it is not clear that reactor-grade plutonium can be used
to make a weapon and statements that it can should not be made.
If spent fuel from thermal reactors is not reprocessed, it has to be
buried in a repository (so also throwing away valuable unused uranium).
The plutonium (also valuable) is buried with it and is hardly secure. Reprocessing
is not only sensible and safe, it is the only way to make sure that the
plutonium is used up and removed from the environment.
Steuart Campbell Edinburgh
Letters: Little leaks
I refer to the article in your 26 February issue by Fred Pearce entitled
‘Britain’s other dam scandal’.
I must ask for space to comment on just a few of the matters raised.
We are told in a bold crosshead that the Victoria Dam is leaking. In
the text which follows however, we understand that it may not be the Victoria
Dam but perhaps somewhere else in the catchment or perhaps again some other
dam. However, the clear intention is to suggest that there is a major problem
at the Victoria Dam – which is most certainly not true.
It is further mentioned that in 1983 the Victoria Dam site was grouted
extensively and a special drain and sump now cope with the problem as if
this was all done as a response to an unforseen problem. This again is
nonsense. The original tender drawings prepared in 1979 clearly show that
substantial grout curtain was always envisaged, as also was a drainage tunnel
and a sump to enable seepage under the dam (which any dam engineer knows
will occur) to be pumped out.
In planning the dam, provision was made for pumps to handle automatically
the seepage into the drainage system below tailwater level (that is, where
simple gravity flow could not be used). At present one pump operates once
a day to empty the sump to deal with seepage flows of less than 5 litres
per minute. This is approximately 1/70th of what the system was designed
to handle. The total leakage past the dam (gravity + pumped) amounts to
42.5 litres per minute at full reservoir, which, for a dam 122 metres high
sealing a valley 500 metres wide, can only be described as insignificant
and surely not justifying the crosshead ‘Leaking Victoria’.
It is also implied that the switch of priority from irrigation to power
at Victoria was made against local advice and has damaged the interests
of the country. The rigorous economic evaluation which was carried out in
1978 demonstrated that the overwhelming benefit of the project was power
– with irrigation benefits contributing only 6 per cent to the total benefits
due to existing and shortly-to-be-constructed storage capacity of the system
downstream. Power shortage was a major problem at the time. It was common
to have six to eight hour-long power cuts every day. The Victoria project
added 40 per cent to Sri Lanka’s installed capacity and led to the virtual
disappearance of power cuts.
The article implies that the Samanalawewa dam has been an ‘enormous
blunder’ and will become an ‘archaeological site’ and a ‘write-off’. It
may be of interest to note that this ‘write-off’ has been steadily producing
energy to the grid for the last year, contributing 411.5 gigawatt hours
which is no less than 95 per cent of the originally planned firm output
to the system.
The leakage which developed through a hillside adjacent to the dam amounts
to around 2 to 2.5 cubic metres per second. This has to be compared with
the requirement to discharge 1.5 to 2 cubic metres per second through the
dam as compensation flow for riparian interests downstream. The actual water
loss for the purpose of power generation is at present therefore around
0.5 cubic metres per second or less than 3 per cent on an annual basis.
When the leak first developed there was a natural concern of the local
population as to the safety of the dam. An international panel of experts
was appointed by the government of Sri Lanka to inspect the site and advise
on remedial works. The unanimous opinion of the panel was that the dam was
completely safe and operating normally and they endorsed the proposal of
the engineers that the leakage could best be dealt with by ‘wet blanketing’
the short section of the river bed in the reservoir which had been identified
as the source of the leakage.
Other inaccuracies and distortions abound in the article. When a problem
of heavy leakage into the power tunnel occurred during construction, we
are told that the problem was only solved by ‘lining the tunnel with concrete
– an extremely expensive business’. The tender drawings always showed that
the tunnel would be lined with concrete throughout its length and that is
precisely what was done.
I am alleged to have said that the ‘supervising engineers failed to
make a detailed site investigation of the dam’s right abutment in 1986′.
I said no such thing. Indeed, a more detailed investigation of the dam’s
right abutment was made by the Japanese in 1986. What was not possible to
do with the budget available at that time (because no contracts had as yet
been entered into by the parties) was to extend the detailed investigation
further along the hillside. Since the Russian investigations had already
covered the area, it was agreed to rely on that information for the time
being, but to check it in detail when preparing the final cut-off design
during construction.
The comments regarding the decision to move the right abutment of the
dam are also incorrect. The small adjustment to the alignment was to exploit
a potential saving in costs which was indicated from the additional drilling.
The move was not – as stated in the article – ‘to get the shortest distance
between the two abutments’ – in fact it slightly increased the distance.
And why it can be said that the move was ‘an enormous blunder’ is incomprehensible.
It is beyond doubt, however, that the move made no difference whatever to
the leakage which occurs half a kilometre away downstream.
I could continue to describe the many other distortions in the article
– but from the few illustrations I have mentioned above I will leave it
to the readers to decide whether truth and integrity have been well served.
Both Victoria and Samanalawewa projects have been and will continue
to be great assets to Sri Lanka, providing power and water for irrigation
well into the next century and probably beyond. Between 1984 when the Victoria
project was first commissioned and February 1994, the Victoria and Samanalawewa
projects have contributed no less than 23 per cent of all the energy produced
in Sri Lanka over that time. For the first two months of 1994, the contribution
has been 34 per cent of the total system demand.
Paul Back Sir Alexander Gibb amd Partners Reading, Berkshire
Letters: Sunken subs
There is a major omission from the map that accompanied the article
on potential contamination risks from sunken nuclear submarines (This Week,
12 March): the wreck of a Soviet nuclear hunter-killer lying 70 miles southwest
of Land’s End.
The vessel, a unit of the first class of Soviet atomic subs, code named
November by NATO, sank on 13 April 1970, apparently breaking up – a pattern
characteristic of hull failures in Russian submarines – and its wreck
has lain on the seabed ever since.
For some years, the Red Navy maintained a Don-class submarine support
ship on station over the location of the sinking. Whether this was to monitor
contamination, deter NATO salvage efforts, or carry out salvage work of
their own, is not entirely clear.
In addition to its reactor, the boat would have probably carried torpedoes
with nuclear warheads, totalling about 20 per cent of its complement of
20 to 25 weapons. Presumably these are still in the sunken vessel’s hull,
unless the Soviets managed to retrieve them.
Although not certain, it is probable that the USS Thresher was also
carrying tactical nuclear weapons, being the first vessel fitted with the
SUBROC atomic depth charge. If so, these weapons presumably buried themselves
in the seabed, along with her reactor, where they remain.
In addition to these warheads, plus those on the Yankee-class boat that
sank in 1986, there are three atomic missiles aboard a Golf-class sub lost
off Hawaii in 1968, plus at least a dozen unrecovered atom bombs lost from
various US aircraft since 1950, lying under the sea.
Hadrian Jeffs Norwich
Letters: Canned gas
Q: We often hear that Freons in aerosols and refrigerators can be damaging
when they are released.
Before these gases were utilised in containers, where did they exist?
John Allsop Rayleigh, Essex
Letters: Lesson from history
I am a student currently studying for GCSE examinations and I have found,
surprisingly, that history requires more scientific thinking, methodology
and observation that the traditional science subjects: physics, chemistry
and biology.
In history, historical pieces of evidence are analysed, interpreted
and compared to other evidence to form conclusions in a logical scientific
manner – like the results of a scientific experiment. We are told to consider
evidence in terms of how it is limited and how different factors have changed
its content, and how this affects the validity of the conclusions made from
the evidence, as one would consider experimental variables in science. Because
history is like this, it encourages individual thought and promotes interest
in its students.
However, in science lessons we merely sit and receive dictation. We
are not encouraged to understand, question or find out for ourselves the
facts that we are given; we are just told to ‘learn it for the exam’. Admittedly,
we do sometimes carry out experiments, but we are never told to design our
own, and are given instruction sheets telling us exactly how to carry out
the experiment – hardly a way to stretch our minds and get us to think scientifically
about problems as we can in history.
Because science lessons do not encourage individual thought or interest
beyond the syllabus, many students of science find it dull and so do not
pursue it beyond GCSE. I feel that the way we are taught science should
change, concentrating less on facts and formulae and more on scientific
methods and thinking for freer and more interesting learning.
Oliver Pawley Kingsbridge, Devon
Letters: Floating on air
Q: Water vapour is 800 times more dense than air, and ozone nearly twice
as dense. Yet water vapour floats in cloud layers, and oxone in a layer
up to 50 kilometres high. How?
Ian Tresman Borehamwood, Hertfordshire
Letters: The flakiest snow
Q: How do wnowflakes know how to be symmetrical? Are there any circumstances
in which they can be persuaded to be asymmetrical?
Sophie Grillet London
Letters: Moon's up
Q: I am confused by the appearance of a gibbous Moon. On Monday 31 January,
I was driving eastwards at dawn towards the rising Sun. Through the side
window of my car – about 120 degrees to the right – I could see the Moon
with its fuller surface directed towards the sun.
Well, not quite. The Moon was tilted a few degrees upwards and did not
present its illuminated face slightly downwards or horizontally as you might
expect.
I confirmed the tilt of the Moon against a nearby vertical pole, as
did my wife who was sitting in the passenger seat. She dismissed my protestations
with a throwaway: ‘I expect that it is an optical illusion’.
Maybe it is, but how . . . and why?
John Grandage Cambridge
Letters: Here we go again ..
As promised last week, here are even more queries to help kick off
New 杏吧原创’s questions and answers section. The response so far has been
wonderful, and we are relying on you to continue sending in answers to
all the questions that we pose and even more questions to help keep us going.
We aim to bring you the first set of answers before too long. Don’t forget,
we are offering a 拢10 book token to the author of each answer that
we publish.
Letters: Vaches enragees
In the 1912 edition of Dictionary of Phrase and Fable (E. Cobham Brewer,
Cassell and Co., London) appears the following:
‘To eat the mad cow. A French phrase, implying that a person is reduced
to the very last extremity, and is willing to eat even a cow that has died
of madness . . . (‘Il mangea de cette chose inexprimable qu’on appelle de
la vache enragee’ – Victor Hugo: Les Miserables.)’
Not only does this imply folk memory of a hazard associated with eating
the flesh of a mad cow, but it suggests that our Continental colleagues
know more of this matter than they are currently admitting. Unless, of course,
cows in France succumb to madness for different reasons than British cows.
In which case, vive la difference.
John Ashby Cheshire
Letters: Jupiter's revenge
Some mistake, surely. The two illustrations showing the relative views
of Jupiter from the Earth and Galileo at the time of impact by SL-9 are
incompatible. They suggest that moving clockwise from the Earth viewpoint
(as seen from the north) involves a parallax shift of Europa in the opposite
direction. As Europa is shown behind Jupiter from the Earth’s direction,
it should appear to move in the same direction.
Similar problems appear with the other planetary positions.
Yours pedantically,
Mike Stevenson Millom, Cumbria
Letters: Jupiter's revenge
I was reading your article ‘Live crash from Jupiter’ (5 March). I understood
that Jupiter’s mass was just short of that required for self-ignition, which
would enable it to become a second sun. I hope experts have taken into account
the possibility of artificial ignition in this respect, for the last thing
we want is for tens of millions (or perhaps hundreds of millions) of people
getting eye trouble due to observing the event under magnified conditions.
The same goes for costly, delicate detection equipment, Hubble, etc.
D. Pennington Southend-on-Sea, Essex