Letters: Glowing gold
Andrew Haynes (Letters, 15 February) has brought up an interesting and
quite well-known phenomenon: the clue is that a normal fluorescent tube
is only light for short periods 100 times a second.
The initial light produced by the discharge in the mercury vapour is
blue, with a strong ultraviolet compound. This is the blue that Haynes observed.
The ‘gold’ is the orange afterglow of the fluorescent coating in the tube.
The blue is only visible for a short time every hundredth of a second. While
the orange is seen a short time after this, it continues for a while after
the discharge is extinguished. Here, if a rotating mirror (at 3000 rpm,
or sub-multiple) is used to reflect the opponent white light and the position
of the mirror is adjusted correctly, first blue then ‘gold’ is seen.
Eric Turpin Lewes, Sussex
Letters: It phollows
Sulfur!
Fosforus?
J. E. Chester St Helens, Merseyside
Letters: Pressure on planes
I refer to ‘Life, the Universe and (almost) everything’ about air travel
(22 February). The centre box states ‘the underwing air force is greater
than that above’. This necessarily brief statement, while correct, obscures
much of interest.
It is more illuminating to talk of air pressure on a wing rather than
force. Most people don’t realise that two thirds of the lift comes from
reduced pressure on the top surface and only one third from increased pressure
underneath.
Most don’t know either how very small the differential pressure is.
A Boeing 747 taking off at 400 tons supported by 5500 square feet of wing
area requires only 1 lb per square inch. Two thirds of that, on the top
surface, is about 16 inches of water pressure; or what a child achieves
with a drinking straw.
F. G. Grisley Barry, Glamorgan
Letters: Advance warning
Due to last minute editorial changes, my Talking Point (29 February)
did not make clear the important contrast between the views of the European
Commission and British Health and Safety Commission on the requirements
of Directive 618/89/EURATOM. The European Commission advises that the entire
population of Britain should receive advance information about radiation
health risks and protective measures, but the HSC is proposing that such
information should be restricted to small areas around licensed nuclear
sites.
Furthermore, a number of errors were introduced into the discussion
about radiation dose limits and HSC’s definition of a radiation emergency
countermeasures.
Readers interested in receiving a full critique of the HSC’s proposals
should write to me, c/o the Nuclear Policy and Information Unit, Town Hall,
Manchester, M60 2LA
Fred Barker Walsden, West Yorkshire
Letters: Radiation records
Feedback (15 February) appears to have been misinformed. The National
Registry for Radiation Workers does indeed contain records of employees
at Sizewell Power Station. However, an individual’s information can only
be made available to the National Radiological Protection Board with his
or her consent. Records of all employees who have given consent have been
transferred to the NRRW. The NRPB decided, however, that coverage of the
Sizewell workforce was not adequate and therefore omitted the station from
their analysis.
You also appear to have missed the reference in our press release to
the significant association between leukaemia mortality and radiation dose
which was found in the analysis. Radiological protection is based on the
assumption that such a risk exists.
Finally, you say that Sizwell A is one of the few Nuclear Electric sites
where a leukaemia cluster was discovered. The question whether or not there
might be a cluster of adult leukaemias near the station was exhaustively
discussed at the Sizewell B Public Inquiry. It was concluded that there
was not. Nor has there ever been a cluster of childhood cases in the vicinity.
G. A. Harte Nuclear Electric Bristol, Avon
Letters: Crypto-chaos
Jim Lesurf describes a seemingly neat idea, namely using a chaotic function
to generate pseudo random numbers for use in cryptosystems (‘A spy’s guide
to chaos’,1 February).
There are just two problems: it’s not original and it doesn’t work.
As a result of the publicity that ‘chaos’ has received recently, its
possible use in cryptography has been researched by a number of people over
the past few years.
One basic property of such functions is that they have very high gain
and so, when they are implemented in fixed precision arithmetic, the rounding
error quickly comes to dominate. They therefore behave very like random
functions, and it follows from undergraduate probability theory that where
the arithmetic is carried out with 2n bits of precision, one can expect
iterates of the function to cycle with a period of about 2 to the power
n. Published computer trials confirm this expectation quite precisely for
the particular function mentioned in the article. Conventional pseudo-random
number algorithms give much longer cycles for a given investment of computational
effort, as well as much greater confidence in their resistance to analytical
attack.
Cryptology is, unfortunately, a subject in which it is a great deal
easier to imagine one has expertise than to actually possess it. Systems
are often designed, and research papers written, by people who have clearly
not taken the precaution of first reading the current research literature.
The result is that many computer and communication security systems on the
market are weak to the point of triviality.
Ross Anderson Computer Laboratory Cambridge
Letters: Fell into a dream
in particular the examples of creativity involving Kekule’s revelation
of the structure of benzene and Coleridge’s poetry (‘The thinking woman’s
guide to the mind’, 18 January). In ‘transcending disciplinary boundaries’,
one has to be careful to get one’s facts right. Just for the record:
Kekule did not have his dream while dozing in front of the fire. He
was travelling on a bus to Clapham at the time, and later wrote: ‘And lo,
the atoms were gamboling before my eyes . . . I saw frequently how two smaller
atoms united to form a pair; how a larger one embraced two smaller ones
. . . I saw how the longer ones formed a chain . . . The cry of the conductor
‘Clapham Road’ awakened me from my dreaming, but I spent part of the night
in putting on paper at least sketches of these dream forms.’ This makes
Kekule perhaps the least typical ‘man on the Clapham omnibus’.
As to The Ancient Mariner, we may not know how Coleridge came up with
the imagery for his poem, but we do know how he came up with the imagery
for Kubla Khan. In this instance, it was Coleridge, not Kekule, who sat
dozing by the fire after taking an anodyne. According to his own account
he had been reading a sentence in Purcha’s Pilgrimage: ‘Here the Khan Kubla
commanded a palace to be built, and a stately garden thereunto.’ He fell
asleep and had ‘the most vivid confidence that he could not have composed
less than two or three hundred lines’. On awakening, he started to write
but was interrupted – not in this case by a conductor but by ‘a person on
business from Porlock’.
John Daintith Aylesbury, Buckinghamshire
Letters: Tropical ozone loss
Mount Pinatubo’s role in facilitating ozone depletion from the action
of CFCs has not been confined to the skies over Europe and North America
(Comment, 15 February). NASA released preliminary findings last month which
indicate that the ozone layer over the tropics – from 10 degrees south to
20 degrees north – was about 10 per cent thinner than normal during January.
This is a most disturbing development. Under a clear sky, a 10 per cent
loss in ozone causes a roughly 20 per cent increase in the amount of ultraviolet
radiation (UV-B) in the DNA-damaging range of the spectrum that reaches
the Earth’s surface. Because UV-B levels in the tropics are high to begin
with (due to the Sun’s direct angle), a 20 per cent increase there represents
a large additional dose of UV-B radiation – over 300 per cent higher than
the absolute increase experienced under the Antarctic ozone hole. The Pinatubo
plume itself may block some of the radiation, but the net effect should
still be a significant increase in UV-B reaching the tropics.
As you point out, few people go sunbathing in Europe during February,
so an Arctic ozone hole may give Europeans only a slight additional risk
of getting skin cancer. However, many Europeans do regularly head to the
tropics during February to bask in the Sun’s rays. Of greater concern are
the millions of tropical residents, along with their agricultural systems
and some of the world’s most diverse natural ecosystems, that face unknown
risks from the ozone loss.
Brad Hurley Global Environmental Change Report Arlington, Massachusetts
Letters: Nappy wearers only
There has been correspondence on the subject of career prospects for
graduates in science. Perhaps I could put in a mention for those of us who
are a little bit older?
I left the Science and Engineering Council a few years ago to return
to Plymouth and got a post very quickly at the Plymouth Information Technology
Centre. I taught computer literacy to adults and youngsters.
My classes proved very popular and we started running classes in word-processing
and other computer applications and our trainees achieved good qualifications.
The government started to reduce the budget for computer training programmes
and the ITeCs were among the first to suffer. Despite having a great impact
on the local economy, our ITeC was forced to merge with a local training
centre.
The relentless reduction in funding eventually forced the training centre
to ‘merge’ with the local College of Further Education. Unfortunately, our
high standards of training were not appreciated by the new board and my
department was closed before the ‘merger’ and all of us declared redundant.
So after 20 years of work in computing I have now been unemployed for
over a year. My applications to the local polytechnic (and elsewhere) went
without response. On asking for the reason, I was told that they wished
to employ someone with ‘contemporary qualifications’.
Please remember those of us who, in our mid-forties, are not even considered
worth interviewing, despite unmatched experience in the field. They only
take people in nappies!
Lawrence Harris Plymouth
Letters: Discrimination
Patrick Trotter highlighted well the problems faced by science graduates
from Northern Ireland (Letters, 1 February). There appears to be very strong
evidence to indicate that a process of discrimination is taking place against
students from this region.
The basis of this claim are the figures for allocations of postgraduate
awards announced in the House of Commons in October 1991. When the figure
for the total number of awards made in the UK is compared to the percentage
of this which went to students from Northern Ireland, a very clear discrepancy
becomes visible. The share given to students from the six counties who were
pursuing science related work was 3.13 per cent whereas for those students
doing social sciences and humanities the share was 9.72 per cent. It may
be that the numbers applying to do science research from the six counties
is a third less than social sciences and humanities. However, the evidence
from Trotter, and from a number of other cases, suggests that a significant
number of science graduates are being turned down for funding.
The Parliamentary Under Secretary of State for Education and Science,
Alan Howarth, is on record as stating that the system for conferring awards
to Northern Ireland residents is ‘confusing and may create difficulties’.
However, as he himself admits, the government has ‘no present plans for
major changes’. Until it, or another government, does, I fear that students
from Northern Ireland, especially science graduates, will continue to be
discriminated against.
Simon Kemp University of Lancaster
Letters: Need for books
We should be very grateful to receive a genuine offer of your old or
new books, magazines, or any library material to augment our new public
library.
We appreciate your sympathy.
A. J. Nyasha 14 Mopane Avenue Kariba Heights Kariba, Zimbabwe
Letters: Face in place
I found Philip Benson and David Perrett’s account of recent work in
the area of digital photographic facial representation very interesting
(‘Face to face with the perfect image’, 22 February). However, I was a little
surprised that the authors didn’t mention the pioneering work in this area
by the New York artist, Nancy Burson.
Working with MIT engineer Tom Schneider in the late 1970s, then with
computer scientists Richard Carling and David Kramlich in the early 1980s,
Burson developed a very interesting computer graphics-based facial morphology
system that is remarkably similar to the one the authors describe. Many
of her findings, including those dealing with the concept of androgyny and
beauty, were similar to the authors’. She also dealt with ageing and was
able to help the FBI to locate missing children by creating aged photographs
of them.
Paul Brown Computers in Art, Design, Film and Television Glebe, Australia