Letter: Latex news
Your contribution on a condom boom and a concomitant shortage of latex
(Technology, 24 March) is guilty of some wild exaggerations. First, the
price for natural rubber latex is no longer ‘phenomenal’: after a price
boom about 18 months ago, prices have returned to normal and are probably
somewhat less than small farmers in Southeast Asia deserve. Current prices
for latex concentrate are around Pounds sterling 810 per tonne.
Secondly, although condoms form an important market for latex, the volume
of latex used is small when compared with that used in the manufacture of
the many types of glove: household, medical and industrial. It is the vast
expansion in the market for medical gloves (based on a growing awareness
of AIDS and other blood-related infections) which caused a brief boom in
latex prices.
Lastly, although it is good to see a reawakening of interest in a natural
product, it would appear to make better economic sense to explore markets
for trans-polyisoprene (perhaps a return to its former role in golfball
covers, for instance) rather than to become involved in the relatively costly
process of isomerising the balata into a possibly inferior form of natural
rubber.
Kevin Jones The Malaysian Rubber Producers’ Research Association Brickendonbury,
Hertford
Letter: Speed of light
The question of photons travelling ‘faster than light’ (Science, 7 April)
is surely just a matter of terminology. The value which we call c, the absolute
limit to observed speed, is the speed at which any particle with zero rest-mass
(such as a photon) would travel in ‘free space’.
We are all familiar with situations where light travels slower than
c, through air or glass, for example, and this is the reason for refraction.
All that is really being said is that true ‘free space’ probably does not
exist, and that what we call a vacuum has a tiny, but non-zero, refractive
index, due to its being filled with virtual matter.
It is slightly misleading to call c the ‘speed of light’: it can cause
great confusion, for example, when trying to describe Cerenkov radiation
(radiation emitted by a particle which travels through a medium faster than
the speed of light in that medium).
I suppose we’re stuck with it though, unless someone can come up with
a catchy alternative. We have to get clear that c is a theoretical limit
to speed, determined by the basic properties of the Universe. It just happens
also to be the speed at which light would travel, if only it had the luxury
of a completely unobstructed path.
Tim Bierman London, NW4
Letter: Dice person
I read ‘A random walk in arithmetic’, 24 March, with interest even though
I am a mathematical tyro. I was puzzled by the conclusion. Why should God
be limited to whole numbers? Why should he be accused of playing dice when
the arithmetical constraints placed upon him are man-made? The proposition
seemed to be returning our thinking about 2450 years to the days of Zeno’s
paradoxes, when it was impossible to prove that Achilles could overtake
a tortoise because fractions had not been invented (or at least their notation).
Sheila Cromwell Waltham Abbey, Herts
Letter: Negative resistance
Jim Lesurf in ‘The rise and fall of negative resistance’ (31 March)
states that some workers working with superconducting oscillatory circuits
have found that such oscillation ‘persists indefinitely without getting
any smaller’. Heaviside, in his Electromagnetic Papers, took the contrary
view, that resistanceless circuits were not necessarily loss-free, and indeed,
in oscillatory circuits, loss was to be expected.
Heaviside’s argument is highly plausible. No material is infinitely
rigid, and so it will deform periodically because of the oscillatory electrostatic
and magnetic forces in the circuit. Such deformation will be accompanied
by small temperature changes as in an ideal gas with oscillatory compression
and rarefaction. Even if the materials of the circuit are ideally elastic
there will still be losses because of the cyclic temperature changes. That
follows from the Second Law of Thermodynamics. In the superconducting circuit
envisaged, there will be excellent thermal coupling between the circuit
and the cryostat, providing a best possible route for the heat to be lost
from the circuit.
Was Heaviside wrong, or was the experiment discontinued before the difference
between zero decrement and very small decrement could be observed?
Chris Parton Glasgow
Letter: Thought for food
The article ‘Famine before the floods?’ (31 March) presents a very narrow
view of the world’s food situation. It fails to note many factors which
probably are more significant than those identified in the article.
Perhaps the most important influence on the food supply over the next
10 to 20 years will be the current collapse of the communist/Marxist/socialist
governments. It is generally accepted that the appalling economic policies
of these countries have greatly retarded agricultural production. It seems
reasonable to expect substantial increases in food production as they move
to the free market.
Lester Brown argues that we are reaching the limits of what science
and technology can do to improve food production. This attitude echoes that
of a century ago when some people said that all of physics had been discovered.
New 杏吧原创 regularly publishes articles on the revolutionary changes
taking place in biology and biotechnology: who is to say that many small
advances in this area will not have a significant cumulative effect on food
supply? Water use can be reduced substantially with modern techniques of
irrigation. Perhaps this is a partial cause of the reduction in per capita
water use in the 1980s noted by Brown – though I see no logic in his apparent
belief that this conservation of water is bad. Considerable room for improvement
exists in the distribution of food, especially in the communist countries;
much food is lost to spoilage.
The list of possibilities for increasing the world’s food supply really
is endless.
Roland Hirsch Germantown, Maryland, US
Letter: Sexist blunder
The letter on women in science from Steve Beackon of AEA Technology
(24 March) made me groan in despair. The whole exercise of trying to integrate
women into what used to be thought of as men’s work is part of trying to
get men to comprehend that women are equal human beings and therefore have
equal rights.
Yet here is this employer, thinking how wonderfully broadminded and
farsighted he is being, but betraying his outlook with the words ‘combine
a career with their domestic responsibilities’. He has evidently never for
a moment considered that a male scientist might have equal domestic responsibilities.
I am now 71, and very sad to think that I am going to die before women
are really equal.
Caroline Sassoon Fowey, Cornwall
Letter: Animal bill
Ursula Mittwoch is to be congratulated on her thought-provoking and
clearly reasoned assessment of the present-day animal politics impasse (‘Animal
rights; human wrongs’, Forum, 3 March).
The centre party suggested by Mittwoch in fact came into being prior
to the passage of the Animals (Scientific Procedures) Act 1986 with the
alliance formed by the British Veterinary Association (BVA), the Committee
for the Reform of Animal Experimentation (CRAE) and the Fund for the Replacement
of Animals in Medical Experiments (FRAME). This alliance held the middle
ground and provided the support the government needed to bring this legislation
to the statute book.
Clive Hollands Edinburgh
Letter: Counting them in
I should like to add the following comments to Tam Dalyell’s Thistle
Diary (31 March) on attendances at the National Museum of Science &
Industry.
The method of counting visitors in the free admission period resulted
in a significant exaggeration of numbers. This is a characteristic of many
free admission museums. Although there was an initial drop, numbers, as
we expected, are now steadily increasing. 281 000 schoolchildren, with escorting
adults, visited the Science Museum in 1989, the largest number ever recorded.
None of them paid to come in because admission for pre-booked school groups
is free. Numbers in free admission school groups are also counted accurately.
Since charging, the Science Museum has used some of its additional income
to open on Sunday mornings, making a total of 55 hours a week. Access is
free from 4.30 in the afternoon until closing time at 6.00, 10.5 hours per
week. 34 per cent of all visitors enter the Science Museum free and a further
31 per cent benefit from a wide range of concessionary rates. In 1988 our
shop at South Kensington was improved and relocated, and a major bookshop
(run by Dillons) has been added. Turnover has doubled.
In the current financial year Pounds sterling 2.48 million (net of all
costs of collection) will be earned by the National Museum of Science &
Industry at its three sites. That income will be invested in improving the
museum and its facilities. Until three years ago the museum made a loss
on its ‘commercial’ activities.
Neil Cossons Director Science Museum, London SW7