Letters: Pretty average
John Chapman (Letters, 15 August 1992) seems to have missed the point
of his own calculation, seeking to demonstrate why a discrepancy can arise
in the average number of sexual partners between men and women. Since there
are twice as many women as men in his village, it is hardly surprising that
the women have half the number of partners on average.
With equal numbers in each sex, however many nuns he includes, the average
comes out exactly where the original article expected – that is, in a population
having equal numbers of men and women, the average number of partners must
be the same for both sexes – despite what people actually tell pollsters.
Frank Everest Stevenage Hertfordshire
Letters: Lead balloon
So ‘American scientists have invented a solid material that is lighter
than air’ which would ‘float away’ if not ‘weighed down by the air trapped’
inside it (Technology, 15 August).
Correct me if I’m wrong, but this would apply to a sufficiently large
lead balloon. It would ‘float away’ if the air inside it was replaced by
a vacuum.
Jim England Kinver West Midlands
Letters: Radioactive fags
If the average uranium content of European cigarettes is 0.07 parts
per million (This Week, 15 August), then British smokers of 25 per day are
inflicting upon themselves sixty doses of X-rays annually in addition to
the other carcinogens in cigarette smoke.
C. C. Woodward Maidenhead Berkshire
Letters: Caught in a web
May I seek an answer to a problem? I live on a narrowboat and am besieged
with spiders who seem to think my craft an ideal residence. Can anyone suggest
a method of deterring the little monsters which is ecologically sound and
harmless to domestic pets and humans?
Constant clearing of the webs and nests has no effect and removal of
the occupants merely creates space for others to move into. Someone, somewhere
must have an idea worth following up.
J. V. Langley Yeading, Middlesex
Letters: Limits to speed
Mick Hamer’s revealing piece on fast cars (‘Beware oncoming traffic’,
8 August) identified the safety benefits of fitting speed limiters to cars,
but not the environmental ones.
First, simply enforcing current speed limits would reduce carbon dioxide
emissions from cars by 3 per cent and similarly cut emissions of nitrogen
oxides. Secondly, restricting the speed at which cars travel could swing
the balance in favour of public transport for many long journeys. Thirdly,
a speed limit would diminish the attraction of large gas-guzzlers, reducing
the average engine size – and thus the energy consumption of the vehicle
fleet.
The European Community’s green paper Sustainable Mobility raised the
possibility of speed limiter legislation. Objections to this tend to be
based on a vague macho desire to be able to ‘accelerate out of trouble’.
The answer, as Hamer makes clear, is not to accelerate into trouble in the
first place.
Tim Brown National Society for Clean Air and Environmental Protection
Brighton
Letters: Limits to speed
You quote a Department of Transport study which found that company cars
were more accident prone than privately owned vehicles ‘presumably because
company cars tend to clock up more miles’.
I owned three cars in ten years before getting a job which provided
a company vehicle. I looked after that one as well, but as time went on
I saw colleagues getting dents repaired at no expense to themselves and
I became more casual. The faster I travelled the more time I would save
and was not that after all the reason why they had given it to me?
Six cars and twenty years later I had bent five of them in accidents
simply by going too fast. Fortunately, no one was injured except myself,
and the vehicles were not beyond repair. I was lucky.
Now driving my own property once more I can instinctively tell from
the behaviour of vehicles in front (and some in the mirror) those which
are not being driven by owner drivers.
J. A. Pearson Hawkhurst Kent
Letters: Growing pains
Diana Brown is entirely right (Forum, 8 August 1992) to express concern
at the potential for ecological damage through uncontrolled population growth.
As good an example as any is the United Kingdom, whose population has expanded
from 4 million to 60 million in only 200 years. This has resulted in an
average population density of 363 persons per square kilometre, compared
with India at 247 per square kilometre and Kenya at a mere 39 per square
kilometre.
The ecological toll can be seen in the 75 per cent of UK land area devoted
to food production (replacing a diverse native flora with a homogeneous
commercial one) as well as in the 11 per cent of land devoted to housing
and industry. Most native mammal species have been severely depleted and
the largest – including the wolf and bear – are extinct. A mere 9 per cent
of the country’s land surface is forest, less than half of India’s 23 per
cent.
The central message of Brown’s article is that we must ‘all pull together’
in reducing population growth and the resulting ecological exploitation.
The annual growth rate of Kenya’s 23 million is indeed high at 4.0 per cent
and India’s 822 million is growing at a fast 1.9 per cent per annum.
However, the annual growth rate of the United Kingdom’s environmentally
profligate 60 million is 2.4 per cent. We must indeed all pull together,
starting where the talk is loudest.
Stuart Nelson The Centre for the Study of Health Brunel University Uxbridge,
Middlesex
Letters: Dental shocker
The article on amalgam fillings (Forum, 1 August) did not refer to the
phenomenon of oral galvanism. In saliva each metal filling acts like a small
battery in the mouth, constantly discharging hundreds of millivolts into
the body.
Some researchers implicate these currents in causing fatigue, migraine,
sleep disorders, eye shimmer, palpitations, depression, and even stress
on the immune system.
This is not to suggest that all amalgam fillings should be removed,
as drilling releases mercury vapour, which can open up another Pandora’s
box of malaise.
It is advisable to have the polarity and current of each filling measured
to see if replacement is warranted, and to have the patients’ compatibility
to amalgam or composites checked before deciding which material is best
to fill a tooth.
Willy Goldberg London
Letters: Common language
It was gratifying to note Martyn Ecott (Forum, 15 August) admitting
that, even in science, English is not such a universal language. However,
I think that he was being slightly pessimistic in his opinion that it would
be unrealistic for everybody to work in one language.
I have just returned from Vienna, where I gave a lecture on the molecular
biology of cancer. Other lectures in the series treated linguistics, melanoma,
astrophysics, the music of the Second Viennese School, and the ecology of
mangroves.
The lecturers came from seven countries and the audience consisted of
people from up to 67 countries. Unfortunately for Mr Ecott and his colleagues,
we did not require translators, since all the proceedings took place in
Esperanto.
Krys Ungar Sheffield
Letters: Sloshing around
In reply to David Nightingale’s suggestion to alleviate sloshing (Technology,
20 June and Letters, 18 July) I should point out that the idea of using
gas-filled bags is already employed in certain propellant tanks on satellites,
primarily as an expulsion method. The difficulty comes when the liquid,
which may have to sit in the tank for up to a decade, is corrosive.
The problem with liquid sloshing is not one of ’empty space’ but one
of compliant surfaces bounding a liquid which is subject to random or periodic
excitation. Even with the gas-filled bags, the underlying problem remains
since the fluid will not be contained by a truly rigid surface but by one
which will have to be deformed if it is inflated. This may reduce the effect
of sloshing but will not eliminate it.
The use of expulsion bags and diaphragms as a means of slosh damping
has been investigated by NASA which found, as expected, that as the tank
size increases, the diaphragm has to be thicker to have a significant effect.
Quentin Vaughan British Aerospace Bristol
Letters: Commercial break
In Feedback (25 July) you refer to a patent taken out for the inclusion
of advertising in software.
You might be interested to know that for several years Clockwork Software
has included advertising breaks in demonstration versions of its programs.
The adverts pop up for a few seconds every five minutes or so, depending
on the type of program. They take the form of a sales pitch by a character
named Nigel.
The industry has dubbed the technique nagware – because the advert’s
principal task is to nag the user into buying a copy of the substantive
program.
‘Nigel’ has provoked quite a lot of hate-mail from users too mean to
buy the software, and even one blackmail threat from a Polish hacker who
wanted to be paid for his time in hacking out the advertising routine!
Jan Worley Clockwork Software Havant, Hampshire
Letters: Fast future
The fast reactor project provides a superb illustration of the problems
affecting British technology and engineering (Comment and This Week, 15
August).
The remark that ‘fast reactors need plutonium and produce plutonium’
is a philosophy that is 20 years out of date. Nowadays the advantage of
a fast reactor would be that it is the only known device (apart from a nuclear
bomb) which can dispose effectively of unwanted plutonium – of which we
have 60 tonnes. This dustbin usage is sufficiently important that even ‘greens’
might approve of reactors for this purpose.
Similarly, the obsession with using liquid sodium cooling is a generation
out of date and our stubbornness has destroyed the economics of such a reactor.
As for accommodating a fast reactor, I would imagine that the group at Dounreay
would be delighted to have a fast reactor sited there.
Ironically, in 20 years’ time we shall probably be buying in fast reactor
technology from abroad as they will wake up to the needs and possibilities
long before we do.
J. D. Smith University of Cambridge
Letters: ET's crossed wires
John Gribbin’s article (Science, 15 August) on the recent work of David
Blair casts doubts on several of the assumptions underlying the search for
extraterrestrial life by radio communication. Blair himself has already
pointed out the possibility that the lifetime of extraterrestrial civilisations
(and ours) may be too short to establish communications if they are driven
to self-destruction with nuclear warfare in a few hundred years. Civilisation
may also collapse due to environmental degradation and overpopulation.
Perhaps, though, Gribbin’s last possibility may apply: other civilisations
may not wish to get in touch with us. A prerequisite for the survival of
civilisations is energy conservation, and large amounts of energy would
presumably be needed to aim radio beams at even nearby stars. ET may have
decided that this is one of the ultra-high-technology activities that it
cannot afford.
Douglas Holdstock Editor, Medicine and War Woking, Surrey
Letters: NASA in a spin
I am baffled by NASA’s tethered satellite experiment (This Week, 15
August). It seems to me that it is a non-starter as a way of generating
power for space stations.
You can indeed generate electricity by cutting a magnetic field with
a copper wire, but as everybody who has had a bike with a dynamo knows,
you have to input mechanical energy to make this happen – you have to pedal
harder. In the case of NASA’s tethered satellite, in order to generate electricity
the tether would have to be dragged through the Earth’s magnetic field,
which would slow the satellite down.
Thrusters would have to be fired to counteract the drag of the tether
and prevent the satellite from losing speed and falling out of orbit. So
all you end up with is a way of converting the energy of the thrusters into
electricity.
A more promising source of energy might be Michael Faraday, who must
be spinning at high speed in his grave.
Annabel Macleod Charlbury Oxon
Letters: NASA in a spin
The attempt by NASA astronauts to launch a tethered satellite from their
craft is difficult to view seriously, though the sheer cost of the endeavour
tends to keep the spectators’ if not the astronauts’ feet on the ground.
This surely must be one of the most bizarre experiments since Franklin
sought to capture electric charge from a thundercloud. It aims to generate
electricity as the tether sweeps through the Earth’s magnetic field.
However, drawing power from this circuit would surely place a drag on
the tether, requiring extra propulsion to maintain orbit. Would it not be
a lot simpler to use the extra fuel to run an on-board generator?
Of course, this wouldn’t be half the fun!
John Allsop Rayleigh Essex