Letter: Life saver
We found Myra McClure’s article on AIDS very interesting (‘Where did
the AIDS virus come from?’, 30 June). However, we need to clear up a misconception
about another virus, feline leucopenia virus.
Contrary to what McClure writes, the virus is in fact virulent in its
natural host, which is why we have vaccines against it. When a canine parvovirus
appeared in the late 1970s, modified live feline vaccine did not kill dogs.
In fact, it saved their lives and was the basis for one of the most successful
cross-species campaigns in the US, Britain and Europe since Jenner’s vaccination
of humans against smallpox using cow pox.
LPM Lloyd-Evans Biobridge Cambridge
Letter: Almost correct
I have noticed lately a rather odd tendency in English usage: certain
words come to be treated with a strange respect, as though like neat alcohol
they will be unpalatable unless diluted. For instance, it seems that one
may not write ‘dangerous’ any more; instead, one must write ‘potentially
dangerous’. I was dismayed to see this homeopathic process carried a step
further in this week’s New 杏吧原创, where in a story about a new AIDS
vaccine (This Week, 16 June), we are told that certain vaccines ‘may be
potentially dangerous’. Now, was the writer quite sure about this?
Quentin Gore Poole Dorset
Letter: Cutting emissions
It is disturbing to read that people with influence in the field of
environmental pollution, like Kenneth Mellanby, ‘are not so sure’ that global
warming is a fact (‘Controlling the greenhouse’, Forum, 23 June). It is
a fact, although the rate of future increase is open to doubt because of
lack of scientific evidence. Sensibly, Mellanby believes we should work
out how the output of greenhouse gases could be controlled and, indeed,
believes that present plans for controlling carbon dioxide are ‘totally
ineffective’. But he underestimates the potential for reducing energy consumption
in Britain when he say it could be cut by ’20 per cent without any serious
effect on our comfort and our industry’. This used to be the figure put
out by the Department of Energy in the mid-1980s.
In April last year, the Energy Technology Support Unit (ETSU) of the
department presented a package of measures to the Prime Minister, which,
if implemented, would reduce the present level of carbon dioxide emissions
by around 50 per cent.
A study of the energy-flow system for Britain, from primary-energy inputs
to final-energy users, reveals that over half the energy content is lost
in the energy-processing industries. Final-energy users probably waste over
half the energy they purchase. So under a quarter of the primary energy
resources performs any useful purpose.
The potential for saving, using existing technology, is considerable
and this should, therefore, be the cornerstone of our policy for reducing
the contribution to the greenhouse effect from Britain.
Mellanby also underestimates the potential for making more use of renewable
sources of energy. The potential for renewable energy in Britain is probably
about 500 terawatt-hours per year, equivalent to more than twice the amount
of electricity we use per year.
It is, therefore, misleading to say, as Mellanby does, that ‘we would
have to depend on a vast increase in nuclear power’ (to deal with the greenhouse
effect). We would not need to.
Fred Roberts Richmond, Yorkshire
Letter: High seas
Norman Cross and Jonathan Scawin are of course correct that floating
ice cannot contribute to a rise in sea level when it melts (Letters, 23
June). They will be glad to know that no professional estimate of the rise
includes such an effect.
The main causes of sea-level rise under a warmer climate will be increased
melting from the Antarctic and Greenland, increased melting from smaller
glaciers, and thermal expansion of the sea water itself. Increased snowfall
on the Antarctic, and possibly on the higher parts of Greenland, may partly
offset this rise.
There may be genuine confusion on several points. First, the popular
press often describes the floating sea ice in the arctic as the ‘Arctic
ice cap’ while glaciologists use ‘ice cap’ for a kind of land-based glacier.
Secondly, large parts of the West Antarctic ice sheet are floating in the
form of ‘ice shelves’ and are not included in estimates of sea-level rise,
although they are very important for the dynamics of the West Antarctic.
Thirdly, floating sea ice is very important for the general circulation
and climate of the Earth even if it does not contribute directly to sea-level
rise.
The latest estimate of sea-level rise caused by the greenhouse effect
is by J. Oerlemans and R. A. Warrick in a report to the Intergovernmental
Panel on Climatic Change (IPCC). They foresee a rise of less than a metre
by 2100, but even such a small rise could threaten low-lying land. However,
such estimates give only the most likely dimension of the problem and must
be followed up by further work.
Glaciologists from Austria, Denmark, Germany, the Netherlands and Switzerland
are now cooperating on glacier-climate studies in Greenland to get a better
estimate of Greenland’s contribution to sea-level rise.
Roger Braithwaite The Geological Survey of Greenland Copenhagen, Denmark
Letter: Hype factor
Your report on the recent factorisation of the ninth Fermat number makes
misleading use of comments attributed to me (This Week, 30 June). I have
absolutely no disagreement with the other mathematicians mentioned, who
are joint authors of a recent paper on the new method, together with HW
Lenstra, of the University of California, and myself.
It is journalists writing on this topic who, in my experience, ‘always
say the same thing’. They always talk as if the difficulty of factoring
a number depends only in its size – so you tell us that 155 digits is a
new record, improving on the previous record of 100 digits. But the circumstances
were different: we cannot have a single meaningful record in this area.
It is the smaller figure which is more relevant to the RSA code.
John Pollard Reading, Berks
Letter: Vet training
I was delighted to see the article ‘American biology student sues over
dissection’ (This Week, 9 June). It is urgently important that educational
institutions practise and instil humane values. A growing number of American
students are refusing to harm animals in the course of their formal education.
The article, however, contained several errors. In reporting that medical
students at the University of California at Davis sued the school over dog
surgery, the author confused two separate cases.
The first case involved two University of Pennsylvania veterinary medical
students. I was one of these students. In 1986, a classmate and I requested
alternatives to several survival surgery laboratories involving the killing
of two healthy dogs. We did not ask to be exempted from surgery, only from
using and destroying healthy animals.
After we were failed for refusing to participate in the course, we filed
a lawsuit to prevent the school from expelling us and to obtain an ethically
acceptable alternative. In May of 1987, the case was settled out of court,
in our favour: the university granted us an alternative that we had suggested
nearly a year before. We completed the course’s requirements by performing
terminal surgery on two companion dogs who were dying of naturally occurring
illnesses.
The second case involves Nedim Buyukmihci, a veterinary ophthalmologist
at the School of Veterinary Medicine, University of California at Davis.
Buyukmihci filed suit against the university in December of 1988, after
the administration initiated disciplinary action against him. The university’s
action arose from Buyukmihci’s granting humane alternatives in an ophthalmic
surgery course he was teaching.
Unlike Britain’s veterinary medical schools, those in the US have a
policy of teaching surgery by using healthy animals purchased for the purpose.
After surgery (with or without a recovery period), these animals are killed.
Increasingly, however, American students and faculty are looking for ways
to reduce or eliminate the destruction of healthy animals.
To date, six US veterinary medical schools have granted alternatives
to students who have requested them. Another three schools are currently
considering student requests for alternatives. Some veterinary schools have
already significantly reduced the number of live animals used. As has been
shown in Britain, it is possible to become a veterinarian without harming
animals.
Eric Dunayer Association of Veterinarians for Animal Rights Old Bridge,
New Jersey, US
Letter: Plucky saying
Albert the Rat was perceptive as ever in ‘taking precautions’ (23 June).
Can he tell us whether the ancient system of a priest behind an altar, with
a chicken, is the origin of risky ventures being done ‘on a wing and a prayer’?
Richard Buxton, Cambridge
Letter: Gas leaks
British Gas’s claim that natural gas has ‘significant environmental
advantages’, with an overall fuel-cycle contribution to the greenhouse effect
from carbon dioxide and methane emissions ‘approximately half that from
coal’ should not go unchallenged (Letters, 12 May).
In reducing from the 38 atmospheres high-pressure mains to 2 atmospheres
and under in local distribution pipes, gas is routinely released at the
pressure reduction valves. Further unknown amounts leak form old, corroded
and cracked pipes.
While British Coal has detailed figures on methane vented from coal
mines, no one knows how much is vented from North Sea gas wellheads. Government
statistics do show that for the 106 production platforms on 26 gas fields,
there is just one flare tower. As a Department of Energy paper puts it,
gas is generally vented as ‘an operational and economic choice’ from all
the offshore filters, condensers, pumps and metering equipment.
Since methane is many times more potent a greenhouse gas than carbon
dioxide, these leaks are important contributors to the environmental equation.
In most cases, gas comes out worse as a fuel than coal according to my published
calculations, and I challenge British Gas to prove otherwise.
Max Wallis University of Wales Cardiff
Letter: Sticky point
It was with a sense of dismay that I read the article ‘Breaking the
mould’, 9 June. An error in the text was the classification of epoxy and
polyurethane resin systems as thermoplastic materials, while correctly identifying
epoxy reasons as thermoset materials in the Table.
And to describe pultrusion as a new technique can only mean new to the
author. The original patents were granted in the 1950s. Standard pultrusion
techniques use low-viscosity thermosetting resin systems, not molten systems.
There are very good technical reasons why the continuous production of composites
using thermoplastic resins would not be classified as ‘pultrusion’, although
the standard production machinery could be used in processing the basic
fibre/resin preform.
As a final point, although unreinforced engineering thermoplastics can
be readily reclaimed and reused, the moment they are converted to high reinforcement
content, to reclaim and reuse the materials becomes difficult, if not impossible.
Charles Allbones Fultrex Ltd Clacton-on-Sea Essex