Letters: Spider's spike?
Judy Turner’s upward pointing icicle (Letters, 2 and 16 November) could
be explained as follows.
Spider-web filaments are virtually invisible because our eyes hardly
ever focus exactly on them.
Such a filament may have been anchored on a stone or something on the
bottom of the birdbath, before it was refilled. Dewdrops would form on the
web and eventually run down where they would freeze if the temperature difference
near the ground was just right.
On the night in question, these conditions must have held for a considerable
time, in order to form an icicle pointing upwards at the angle of the invisible
spider web.
J. A. Briscoe Harrogate, North Yorkshire
Letters: Fungus-free
During the Australian summer, most dead organic matter is soon colonised
by fungi. I am struck by the fact that this is not the case for the used
coffee grounds in the bottom of my plunger-type coffee infuser/filter, although
the conditions of warmth and moisture are optimal for fungal growth.
It may be worth investigating this low-technology material for its
possible biological activity.
Timothy Miles University of Adelaide, Australia
Letters: Pointless permits
Michael Grubb sees transferable permits as an essential part of a viable
mechanism for stabilising emissions of greenhouse gases within the EEC (Talking
Point, 2 November). Their basic function would be to encourage the lowest
cost abatement measures to be implemented irrespective of where in the European
Community the opportunity existed. But at the same time he says that ‘stabilisation
is technically feasible without incurring extra costs’. This surely undermines
the case for the permits. If a country can cut its own emissions at zero
net cost why should it be willing to pay money to another country just because
it can do the equivalent job more cheaply? (There may be macroeconomic reasons
for doing so but that is a different proposition.) If countries behave rationally
the transferable permit will only start to fulfil its function once we have
done what is economically viable and move on to what is not. I think we
have enough to do in getting to that point without complicating matters
further.
J. A. Feather London
Letters: Moans about mink
How many carnivores do have natural predators to regulate their numbers?
Very few, I think. Like most carnivores, mink appear to be regulated by
the amount of prey and suitable habitat available. Ariadne’s comment that
‘as mink have no predators, they are increasing in numbers’ (Ariadne, 2
November) is quite illogical.
Mink have been present in the Thames area for at least 10 years now
and there is no definite evidence that they (rather than increased river
traffic) have reduced the numbers of coots and moorhens in the area. Anecdotal
evidence abounds but, as in the many other countries where mink have been
introduced, proof of guilt has never been established and numerous dietary
studies generally suggest that they do less damage to the wildlife than
gamekeepers and mink hunters would have us believe. It is highly unlikely
after all this time that mink numbers are still on the increase in this
area.
Whilst I wholeheartedly condemn the misguided atrocities committed in
the name of animal liberation and believe it to be a great shame that mink
were introduced to this country, I think we should be more cautious in allocating
blame for wildlife depredation on mink. Blame for the decline of otters
in the 1970s was laid on mink as competitors for resources although it soon
became apparent that pollution was taking a major toll on otter populations
– where would the otter be now if we had hunted mink instead of banning
organochlorine pesticides?
Danielle Clode University of Oxford
Letters: Here is there
Dipankar Home and John Gribbin ask whether light is a wave, a particle
or something entirely different (‘What is light?’, 2 November). The nature
of light may well be a conundrum for us matter-bound observers, but when
we consider light from light’s own point of view the wave-particle duality
would seem to disappear.
The special theory of relativity predicts that, for an observer moving
at the speed of light, distance travelled shrinks to zero while time slows
to standstill. Thus, as far as the light itself is concerned, it does not
travel any distance, and takes no time to do so. As Gilbert Lewis showed
back in 1926 (Nature, vol 117), from light’s point of view the Universe
is so ‘bent’ that there is no separation between the point of emission of
light and its point of absorption – hard as that may be for us to imagine.
In its own frame of reference, light is simply an exchange of energy between
two points that are ‘in contact’.
If light does not experience itself to have travelled any distance it
does not need a vehicle or mechanism by which to travel. It has no need
to be either a wave or a particle. It is only in our frame of reference
– the frame of observers with mass who move at sub-light speeds – that light
appears to travel through space and time; and only in that frame does the
question of whether it is a wave, a particle or both arise.
Perhaps the question we need to ask is whether this frame of reference
is the most appropriate frame for trying to understand the nature of light,
which has no mass and moves, quite naturally, at the speed of light. Could
this mismatch of reference frames lie behind our conundrum?
Peter Russell London
Letters: Jobs in water
As a 1990 graduate with an upper second BSc honours in geography, I
would like to draw readers’ attention to the fact that all is not rosy in
the garden of water industry graduate recruitment, as Neil Harris would
have us believe (Careering Ahead, 2 November). Having paid particular interest
to hydrology, coastal zone management and applied geomorphology at Polytechnic
South West, combined with two years’ experience in geotechnical soil testing,
I am still not in the career I wish – the water industry. This, I can assure
you, has not been due to lack of effort or commitment, as I have applied
to over 50 suitable National Rivers Authority vacancies, with only two interviews
in the past 16 months. Opportunities are not as substantial as Harris portrayed,
and despite one’s ‘knowledge and skills’ there is an awful lot of competition
with people equally well-trained.
James Tricker London
Letters: Jobs in water
Neil Harris highlights the relative shortage of skilled physical oceanographers.
To this I would add a shortage of graduates in molecular biology willing
to apply their skills to environmental problems. These problems are often
essentially biological in nature and we urgently need to apply modern biological
procedures in addressing them. The techniques are available, as are the
graduates with the appropriate expertise. We need these young scientists
to become involved with the challenges posed by the aquatic environment.
Brian Bayne Plymouth Marine Laboratory Plymouth
Letters: Pi was pi
Fascinated by A. J. Hoare’s assertion concerning wartime Royal Signals
standing orders on the value of pi (Letters, 9 November), I did a little
checking. My father was a member of the unit in question (3rd Technical
Training Battalion, Huddersfield) from November 1941 to April 1943, and
denies they ever used 3. 22/7 or 3.1416 for specialised purposes, yes, but
3.0, never!
John Dallman, London
Letters: Desert rivers
I read your article ‘Will Gaddafi’s great river run dry?’ with great
interest (This Week, 7 September).
I designed the North and South Sahir Well Fields which have been in
operation since 1974, and which are monitored by a network of monitoring
wells. The recent data indicate the drop in water levels in shallow aquifers
is less than 2 metres in 11 years of operation, and the pumping levels in
the wells are not changing because the water is being supplied from the
upper aquifers.
Our model for the Kufra and Sarir basin indicated that inflow from Tibesti,
Chad and Sudan is 80 m3/sec. The idea of the well field drying up in 50
or 100 years is a pure speculation by people who are not familiar with the
actual data.
The people of Africa are dying of hunger and starvation. It is the duty
of hydrologists to do their best to provide water for the people. There
is plenty of groundwater in the Sahel and North African sedimentary basins
which can be used for agroforestry. We are currently exploiting US groundwater
in California, Nevada, Arizona and Texas and nobody is telling us that is
a ‘national fantasy – it’s madness to use this water which can never be
replaced for agriculture’.
While the initial investment for developing the Libyan irrigational
system is high, I am dismayed that you are advocating supply of American/European
subsidised food to the poor African countries. Rather than spending their
financial resources on imported food, the Sahelian are choosing to invest
in developing their own resources.
Moid Ahmad Ohio University, US
Letters: Militant sceptic
I am often intrigued by the pieces of prose you run which flow from
the sceptical pen of Wendy Grossman (Forum, 19 October). There is more than
a little unscientific militancy to be found in her beliefs and opinions.
The enemies of her attacks are always fringe beliefs, most of which bear
little consequence to the majority of us (such as UFO sightings). Such ferocity
for so little.
I do believe in rationalism and intellectual scepticism, but it might
not be a bad idea if the focus of scepticism advocated by sceptics be expanded
to include their own motivations and practices as well. After all, they
do take on faith that their methods are impeccably rational and that their
ontological beliefs are true. Such certainty does not exist for most philosophers
of science or scientists who have thought deeply about the process of scientific
inquiry itself. Grossman’s diatribes remind me more of religious fundamentalism
than the open-minded process of scientific inquiry. Peter Nelson Griffith
University Brisbane, Australia
Letters: Science in Welsh?
Tony Jones’s piece (Forum, 26 October) does set one thinking. On the
surface, any move to bring more science to people of Welsh-speaking Wales
via Cymraeg is appealing. However, in conjunction with recent moves to make
Welsh paramount across the curriculum in schools, in civic life and more
widely, will it in fact decrease the ability of the population inside this
enclave to access and understand science?
At the close of the 20th century it is obvious that mankind’s effects
on the environment through science and technology can only be addressed
if all people have, at the very least, access to all available information
on which to judge and make decisions. It seems unlikely that the dedication
of those such as Cymdeithas Wyddonol Genedlaethol could provide all that
is necessary.
Tony Jones indicates what is happening elsewhere, even in anglophobic
countries such as France. Like it or not, communication in this crucial
activity occurs largely through the language known as ‘English’.
Peter Drake Bangor, Gwynedd Wales
Letters: Medicinal peas
Further to your correspondence on Useful Things To Do With Frozen Peas
(Feedback, 28 September; Letters, 9 November), may I suggest two more invaluable
tips.
A handful of frozen peas placed in a polythene bag and held gently against
a bruised and battered perineum post-childbirth, is most soothing and effectively
reduces swelling.
Also, later on when the baby becomes a toddler, should nappy-rash be
a problem, a yet smaller quantity of frozen peas in a bag held against the
inflamed blotches on the buttocks brings very quick relief.
Jane Hatt Burgess Hill, Sussex
Letters: Hovering droplets
Mike Petty’s explanation of those mysterious ‘floating’ water drops
is, at best, only partially correct and may be completely wrong (Letters,
2 November).
He quoted an article by C. L. Strong (‘Water Droplets that Float on
Water’, Scientific American, 1976), in which the phenomenon is attributed
to electrostatic repulsion aided by the presence of surfactants. It may
play some part, but a more recent article by Jearl Walker in his discontinued
and much-lamented Amateur 杏吧原创 column (Scientific American, June 1978)
casts considerable doubt on this theory as a full explanation.
Walker claims that a more widely accepted view is that such drops ride
the waves like miniature hovercraft, on a thin air cushion flowing radially
out of a lens-shaped body of air trapped below each drop. This is rather
similar to the Leidenfrost effect, in which drops can briefly rest above
a hotplate on a layer of steam. He describes a series of simple, fascinating
experiments showing that the phenomenon depends more on the surface being
vibrated by small ripples than on the presence of surfactants (in fact it
can periodically be seen on a calm lake lashed by a heavy rainstorm). The
ripples, whether in flicked orange juice or splashing coffee, are somehow
responsible for ‘pumping’ air into the space below each drop. It appears
that the precise mechanism remains uncertain.
How good it must be for the scientific education and motivation of those
commendably curious children at Clifton College Preparatory School, that
they have been able to make an observation for which textbooks and New 杏吧原创
readers have offered no comprehensive explanation. There is more to science
education than the passive soaking up of explanations, and everyone thought
they were just messing about with their orange juice!
Ian Russell New Mills, Derbyshire
Letters: Hovering droplets
Imagine a small sphere of water on the flat surface of a cup of water.
In order for the two to coalesce, both need to increase their surface area
slightly to form a neck where they will join. So surface tension means that
they are in a local energy minimum (albeit a not very stable one). After
a second or two a tiny ripple disturbs them and they do indeed coalesce.
You can do the trick with icebox distilled water containing a tiny amount
of washing up liquid. Drip drops on the surface, and some will skid about
before merging. As always when water is dropped onto water, you will make
some air bubbles in the main body of water which will quickly float to the
surface. Interestingly, you will also make a water bubble in water. This
is the exact analogue of a soap bubble in air: it is a sphere of water with
a thin film of air round it, surrounded by more water. These float upwards
much more slowly. They exist for the same reason as the coffee and orange
globs – to merge with the main body of water they need to increase their
surface area, which requires a tiny input of energy.
Adrian Bowyer University of Bath