Letters: Seeing double
The effect noted by James Neal (Letters, 11 January) sounds like colour
stereopsis. When viewing an image that contains saturated reds and blues,
many observers see the two colours in different planes. This occurs when
the pupils are not exactly centred on the optic axis, so the lens acts as
a prism. Blue is refracted more strongly, so the red and blue images on
the retina are displaced slightly relative to one another, effectively producing
a stereo pair. It is possible to appreciate this effect by a method that
is less enjoyable than an office party, but arguably safer. Using slips
of paper, or your fingers, block the outboard halves of both pupils: the
blue areas will move forward. Conversely, blocking the inner halves causes
the red areas to advance.
Why should alcohol produce this effect? Most people’s eyes tend to diverge
or converge symmetrically when muscular control is weakened. If this ‘vergence’
becomes so great that perceptual fusion is lost, the traditional double
vision of the souse occurs. The case described by Neal was not that severe,
but presumably his pupils drifted slightly off their optic axes.
C. R. Cavonius Dortmund, Germany
Letters: Bad timing
Whilst watching the Lifestyle satellite channel on Astra my son and
I made an amazing discovery: time travel by remote controller. It started
with the contemplation of ‘what time is it at the North Pole’ into the measurement
of the speed of light by measuring the time difference between clocks on
teletext between terrestrial and satellite TV channels. Being accustomed
to setting my watch from the Radio 4 pips or Ceefax I naturally assumed
that the broadcasters would set their clocks to a reliable source. It was
quite a surprise to see an average variation between clocks of around 2
minutes with the Lifestyle clock being 8 seconds ahead. I wonder if anyone
can throw some light on this phenomenon.
Martin Maynard Arborfield, Berkshire
Letters: Weighty mistake
Accept, please, my congratulations to New 杏吧原创 for being the first
to inform the world of a new discovery. Up to now we thought that the periodicity
of a pendulum’s swing is determined by its length. In Technology (11 January)
it is stated that this must be done by adjusting its weight. Are we witnessing
the dawn of a revolution in physics?
Otto Lendvai Budapest Hungary
Letters: Planetary memories
Ariadne (25 January) should have consulted dictionaries of mnemonics
to find the accepted one for the order of the planets from the Sun: ‘Men
Very Easily Make Jugs Serve Useful Nocturnal Purposes’. This does, of course,
differentiate between Mercury and Mars, but the wish to include the Moon
is hardly realistic, given that it is sometimes inside the Earth’s orbit
and sometimes outside. Surely Ariadne does not believe the Moon is a planet?
Storm Dunlop Chichester, West Sussex
Letters: Blow out
I am writing this on board an Intercity 225 Scottish Pullman, currently
due to arrive one hour and 20 minutes late at London King’s Cross. The delay
has been caused by stone-throwing vandals who broke the outer layer of a
double-glazed window. Speed has been reduced because ‘pressure from a passing
train could cause the window to blow out, or in’ the ‘Senior Conductor’
explained.
Which? Would the weakened window blow out, or in?
Christopher Lambton Edinburgh
Letters: Fistful of fungi
As a keen, self-taught mycophage, I found Barry Fox’s article on the
dangers of eating mushrooms very interesting (‘Stalking the safe mushroom’,
18 January). But I do think it gave an unnecessarily gloomy view of the
real risks inherent in eating wild mushrooms.
The vast majority of 3000-plus species of fungi to be found in Britain
are harmless when eaten by humans. A few simple rules can be used to eliminate
the chance of eating the truly dangerous species. When I began looking for
wild mushrooms to eat, I started by picking only boletes – mushrooms with
pores underneath the cap instead of gills – which are also amongst the tastiest
of all wild mushrooms. The one or two dodgy boletes are readily identifiable
by being extremely brightly coloured, and are usually rare. Roger Phillips’s
excellent photographic guide (Mushrooms and other Fungi of Great Britain
and Europe, Pan, 拢12.99) makes spotting the bad guys easy.
I then discovered that the excellent and easily identifiable parasol
mushroom (Lepiota procera – it’s much bigger than the other Lepiota) can
be found in large numbers on old grassland (Royal Parks especially – but
I’m saying no more because I don’t want to diminish my supply this year).
A friend then spotted chanterelles (Cantharellus cibarius) during a
summer woodland walk. The same woodland has also yielded oyster mushrooms
(Pleurotus ostreatus), many species of boletus, and I’ve seen enough fly
agaric to intoxicate several herds of reindeer. All this in a smallish wood
in southwest London.
Above all, I follow one golden rule: if in doubt, throw it out. If I
am not 100 per cent sure of the identification of an edible species, I don’t
eat it. Despite being extremely cautious, one or two woodland and grassland
walks a week during the late summer and autumn make supermarket mushrooms
redundant in this household.
Gareth Renowden Teddington, Middlesex
Letters: Stopping the action
Richard Need (Letters, 21/28 December) questioned the function of the
follow through advocated by coaches and executed by batsmen, tennis players
and golfers.
Stopping the bat immediately after impact would require the muscles
causing the swing to stop acting, whilst the antagonists to these muscles
would have to act as quickly as possible. Rapid activation of the antagonist
muscles would be physiologically unsound, as this would have a high energy
cost, as well as increasing the risk of injury. The gradual activation of
the muscles that presumably occurs when a follow-through is used allows
for the gradual build-up of force in the antagonist muscles, and for gradual
deceleration of the bat.
If the striking action does not require high speeds and therefore high
muscular forces, the rapid stopping of the bat becomes more attainable.
A more rapid stopping is often seen in certain golf shots requiring low
club head speed and low muscular forces. There may be reasons for encouraging
follow-through other than those relating to muscular factors, for example
maintaining balance, and avoiding slowing the action before impact.
A question in a similar vein is what are the mechanisms which cause
enhanced performance as a consequence of a ‘wind-up’ or countermovement
in certain sporting activities. Such phenomena are often seen prior to a
strike with a baseball bat, or prior to a maximum vertical jump.
John Challis Loughborough University
Letters: Counting cancer
It is true, as Phyllida Brown says (This Week, 18 January) that there
are at present no mechanisms for monitoring treatments used by doctors in
Britain. National comparative audit of highly sensitive confidential data
can only be undertaken by an agency that has the trust of those supplying
the data: for medicine that means it must be done by the medical Royal Colleges.
The Medical Audit Unit of the Faculty of Clinical Oncology (cancer specialists)
of the Royal College of Radiologists is working on a system to address this
task, the Clinical Oncology Information Network (COIN). COIN will be a clinical
information system which will enable us to institute national comparative
audit of the work done by cancer centres, along the lines of the successful
scheme already run by the Royal College of Surgeons.
The task of auditing cancer treatment is much more complex than for
surgery, because of the much larger number of variables that must be recorded
in a consistent way. The first step is to create a system specification
for the work of cancer centres. We also have to relate an agreed nomenclature
(a set of accepted terms and their synonyms) for cancer, as our contribution
to the national programme initiated by the NHS Centre for Coding and Classification.
We plan to implement the system on a network of Apple Macintosh computers
to give our clinicians the benefits of their graphical interface. COIN will
have the potential to be used worldwide, creating very large data sets of
the practice and outcomes of routine treatment. It may provide a future
alternative to the randomised clinical trial.
Chris Squire Royal College of Radiologists London
Letters: CD interference
Unbeknown to most of the air-travelling public, British Airways bans
the use of passengers’ personal compact disc players on commercial flights.
Their comprehensive prohibition list includes ‘cellular telephones,
radio receivers as well as transmitters, television sets, compact disc players,
video cameras, video players, remote control toys, and all devices utilising
light emitting diode displays’.
British Airways tells me that this is not for the obvious social reasons
but because of supposed interference with flight deck compasses and warning
lights.
In a recent unsubstantiated ‘case’, an MD-80 aircraft was supposed to
have been rendered temporarily unhandleable after a young passenger started
listening to his portable CD player. Apparently portable tape players (like
the Walkman) are safe.
While it is understandable that those devices with transmitters (such
as the cell phone) can cause problems, can any reader hazard a guess as
to what mechanism causes a low power portable ‘Discman’ CD player to interfere
with a plane?
Simon Gardner Leighton Buzzard, Bedfordshire
Letters: Backwards signals
Rian Hughes draws some interesting points about data transmission, from
his observation that a queue of stationary traffic that starts and stops
at the head of the queue sends a signal backwards of these changes (Letters,
18 January). But I regret to say that he will not make his fortune with
this technique.
A perfectly workable communications link can be made by sending a carrier
signal from one end of a transmission line, end A, and modulating it by
varying the impedance at the other end, B. The changes in impedance affect
the line current, which is easily monitored at the first end. Thus data
is sent from B to A. This is exactly what happens with the domestic electricity
supply. When kettles are plugged in across the country to make tea during
a commercial break, the event is clearly registered by the ammeters at the
generating station.
A similar thing is happening with the queue of cars. The impedance of
the road is changing at the front of the queue and the fluctuations are
observed at the rear, which is providing the source of the vehicles.
It is quite permissible for the carrier signal to be modulated to carry
information from A to B whilst information also travels in the above manner
from B to A. But the two signals must be at completely different frequencies.
Hughes is correct that there is a ‘subtle delay’ of the ‘no current
flow’ signal, in both a transmission line and a queue of cars. In the queue
of cars it is easily observed simply because it is so slow, as it relies
on a complex optical-biological-mechanical link. A second mode of propagation
is possible which is purely mechanical and considerably faster. However,
this mode is only sustainable for one cycle during which it invariably overstresses
the transmission line, and data flow ceases completely whilst insurance
details are exchanged!
Ian McWhirter University College London
Letters: Backwards signals
I too have observed the waves produced when cars begin to move in a
traffic jam, but to me this is analogous to the flow of holes in a p-type
semiconductor. Now if we can find the equivalent of the n-type semiconductor,
it could be inserted in the traffic flow to form the equivalent of a pnp
transistor. This could therefore act as an amplifier, thus speeding up the
traffic.
Could this be the answer to all the traffic problems?
Brian Curtis South Ruislip, Middlesex
Letters: Small but exotic
Jack Cohen’s entertaining article ‘How to design an alien’, (21/28 December)
comments that most science fiction creatures are too much like Earth’s.
Life on another planet would be very different since so many characters
have evolved by a sequence of improbable chances. But he then commits the
same offence by assuming that animals must be part of any life system and
are not themselves just chance productions.
Well, for one thing, life on Earth managed very well for three-quarters
of its history without them. In all that time there were vast numbers of
small but exotic creatures – all you had to do to appreciate them was to
be small yourself.
There are only four really inescapable attributes of any life evolved
by natural selection. These are a nearly stable but slightly mutable store
of coded information (as are DNA and RNA), growth, replication, and some
means of acquiring energy. On the early Earth energy did not come from sunshine
or oxygen but from the inorganic and organic soup, once the enzymes had
evolved to exploit the energy-yielding reactions between its constituents.
This might have continued indefinitely on a dark planet with unlimited soup
rising from its interior. Even on Earth many anaerobic microbes still live
this way in mud, soil, volcanic vents and intestines.
Even with enough radiation available to encourage the evolution of photosynthesis,
various alternative forms can be imagined – producing, say, sulphur, phosphorus
or chlorine instead of oxygen as a by-product, and using different parts
of the electro-magnetic spectrum. Some purple bacteria still use a sulphur-based
photosynthesis which probably preceded the oxygen type invented by blue
bacteria.
It is to be hoped that if there are intelligent beings out there, they
include biologists less concerned than ours with what they can easily see,
collect, dissect and classify, and just as speculative in biochemistry as
in anatomy. They might then know we are living if they meet us. On current
form I doubt if we would recognise them.
Ralph Cooper Hopetown, Western Australia
Letters: Off the record
We appreciate Jeremy Webb telephoning us for comment before completing
his article ‘Police attacked over DNA fingerprinting’ (This Week, 18 January).
But some important ingredients were still wrong.
Webb reported that Liberty, the civil liberties group, had applied to
the European Court of Human Rights in an attempt to force the British government
to lay down in law what powers the police have over DNA fingerprints. We
have not seen any details, but we made a similar point ourselves last November
in our submission to the Royal Commission on Criminal Justice.
The law does need clarifying to take account of modern molecular genetics.
The Home Secretary has authorised the holding of DNA profiles in unsolved
cases, from convicted criminals and from those awaiting trial – and this
is what the Metropolitan Police Forensic Science Laboratory (MPFSL) holds.
Webb refers to the case of a Roy Williams and says that ‘Although Williams
was eliminated from the murder inquiry, the police refused to destroy details
of his DNA profile, which had been added to their computer records. Liberty
took up the case and eventually forced the police to remove Williams’s DNA
profile from their computer’.
First, if Webb obtained this information from Liberty, he ought to have
quoted his source – because this information is wrong. It really is not
good enough for New 杏吧原创 to make assertions about what we put on databases.
Second, the DNA database needs scientific interpretation and it runs on
a laboratory computer; it is not accessible by the police.
Some wires are crossed somewhere and I fear a well-intentioned effort
to add clarity where clarity is needed may founder because Liberty has misunderstood
some issues and it may have picked a poor example for the European Court.
Brian Sheard Metropolitan Police Forensic Science Laboratory London