Letters : Live long, get ill
London
The prevalence of osteoporosis may be increasing but it is
certainly not a modern disease
(15 December, p 42).
Although there is no satisfactory definition
of osteoporosis in human remains, evidence of extreme bone loss is found in
individuals from all periods of human history. This evidence includes cortical
thinning, loss of the thin bars of bony tissue called trabeculae, the occurrence
of typical osteoporotic fractures in the spine and femoral neck, and, much less
frequently, fractures of the distal radius and ulna.
We don’t yet have reliable information on the prevalence of osteoporosis in
early populations, but this is clearly needed before we can decide how much more
common the condition is at present. One explanation for the relatively few cases
in the past may simply be that men and women did not live long enough to develop
it.
Several other supposedly new diseases鈥攔heumatoid arthritis and Paget’s
disease, for example鈥攖urn out to be nothing of the sort once the evidence
from past populations is properly assessed.
Letters : Waste not
Urrbrae, South Australia
Further to your articles concerning the British government’s energy review
(15 December, p 3
and 5),
nuclear power can come in many different shapes and
sizes. The case for large-scale generation of electricity using nuclear power
may be difficult to sustain, both economically and environmentally, but there
could be other ways of using existing nuclear resources.
Several reports have condemned the use of electricity for heating homes. In
Britain,
60 per cent of the available energy is lost in the process of converting the
heat in power stations to electricity and then back again to heat in homes. This
makes little sense, whether the source of the heat is burning fossil fuels or
nuclear power.
At the same time, governments around the world are spending large sums of
money securing and cooling hot radioactive waste鈥攑articularly high-level
waste. Why not consider using this as a domestic heat source?
Rough calculations suggest that two cubic metres of synroc-encapsulated waste
per household in a heating scheme for, say, 100 houses, could provide background
heating (with summer storage) for a hundred years.
Such distributed storage of safely synroc-encapsulated waste would not
attract terrorists or pose a great threat to the environment. Appropriate
radiation shielding would ensure that the only emission from the heating unit
was clean hot water, which would be circulated between houses, a summer storage
system, and the synroc block. There are zero atmospheric emissions associated
with such a system, and the radioactive waste is not only there already but is a
headache for society.
Letters : Wandering star
Edinburgh
Every Christmas astronomers come up with new and not-so-new explanations for
the star of Bethlehem. Michael Molnar was not the first to suggest that it was a
planetary conjunction, but now he claims 4th century confirmation.
It is always unwise for scientists to attempt to explain literature.
Astronomers in particular should beware of trying to explain what historians and
theologians know to be a myth. The star was just one invention among many in the
gospel’s “birth narrative”. It is futile to look for an astronomical explanation.
Readers interested in this topic are directed to Molnar’s book, The Star of
Bethlehem: The legacy of the Magi, Rutgers University Press (1999)鈥擡d
Letters : No-win options
Sandgate, Queensland
In using the name “WinZip” no less than five times, Andrew Watson implies
that the language identification technique described in your article
(15 December, p 25)
is specific to this software. It is actually the ZIP algorithm
that makes the described technique possible.
The ZIP algorithm is the invention of PKWare and the technique described in
this article could equally well be applied using their PKZip software or any
other software utilising the ZIP algorithm, such as DropZip by Aladdin
Systems.
In the extreme, one could even infer wrongly from the article that this
technique is only possible using a computer using Windows, as WinZip is
Windows-only software.
Letters : Kink in common
Caterham, Surrey
Robert Duncan’s study of “moving” volcanic hot spots
(15 December, p 20) was
interesting but flawed. Using only the example of Hawaii’s Big Island, he
suggests that the direction of magnetisation in the Big Island’s lava stack
shows that the underlying hot spot has probably moved relative to the oceanic
crust.
However, the three other main Pacific hot spots鈥擬acdonald, Louisville
and Easter Island鈥攇ive the lie to his theory. The line of the
Hawaii-Emperor seamount chain is identical to that of the austral Cook
Islands-Marshall Gilbert seamount chain. Both are “kinked” at exactly the same
angle at the same time鈥� 43 million years ago. Elsewhere, the line of the
Louisville Ridge seamounts draws the same parallel to that of the Tuamotu
Archipelago. These hot-spot trails have the same distinctive kink, also aged 43
million years. Sampling of the seamounts has proved the ages of the respective
chains, and the age of the “elbow bend” in all.
It seems unlikely that all four hot spots are moving in the same direction
through the Earth’s mantle. It is more likely that they are indeed stationary,
that the Pacific plate did change direction 43 million years ago, and that the
magnetic anomalies noted by Robert Duncan were caused by local disturbance of
the Earth’s magnetic field during intense phases of volcanic activity. The
active Krakatoa, for example, is notorious for disturbing ships’ navigation
systems.
Letters : Stitch in time
Harlow
Regarding your article on crocheting a hyperbolic plane
(22/29 December, p 38):
in Lewis Carroll’s now-forgotten Sylvie and Bruno Concluded,
chapter 7, “Mein Herr” describes the construction of a “purse” with its outer
surface continuous with its inner one, so that “whatever is outside it is inside
it, so you have all the wealth of the world in it”. This was done by filling in
the opening of a M枚bius loop (he refers to it as a Puzzle Ring, as it was
popularly known at the time) with a non-twisted sheet.
I’m not sure whether Carroll was writing before or after Felix Klein’s 1882
publication describing the joining of two M枚bius strips. Although the story
wasn’t published till 1889, in the preface Carroll states that he’d started
writing the story in 1873, and most of the substance was in manuscript by
February 1885.
It does seem to be very likely in any case to be the first description of a
one-sided edgeless surface outside the technical literature, unless Carroll had
picked up the idea from Klein in a popular science magazine.
Letters : . . . . .
Waverley
Meet one rather crotchety crocheter. In trying to follow the instructions on
crocheting a hyperbolic plane, I am forced to conclude either that said
instructions are not quite right, or that I am misinterpreting them.
As I understand them, they are designed to produce a shape commonly resulting
when inexperienced crocheters try to make a flat mat and fail to increase the
number of stitches often enough (by making two stitches into one previous one,
as in step 5). The result is a disc that curves inwardly, becoming less and less
flat as it grows more cup-like.
If this is in fact what is intended, then there are two errors in the
instructions: (i) Step 3 is back to front: if N is larger, the curving will be
more pronounced and the result LESS flat; (ii) Step 6 should require repetition
of steps 4 & 5, not 3 & 4 (why would you change N every time you repeat
the sequence?).
Other than that, this appears a novel and fun way of dealing with complex
mathematical notions.
Due to an error during the editing process, we did indeed introduce problems
for would-be crocheters: if you want to get a plane, the first stitches SHOULD
NOT be joined into a circle. If you join them in a circle, then you get another
type of model, the pseuodosphere, and for that there is no need to do an extra
stitch at the end of the row because all crocheting will go in a spiral.
Go to the letters on our website for information on mathematical wall
丑补苍驳颈苍驳蝉鈥抬诲
Letters : Windscreen blues
Sheffield
The chemists at BASF in Germany haven’t really thought it through. Their
electric blue-tinted windscreen
(8 December, p 21)
will reduce the driver’s
ability to see red traffic lights and brake lights, by inducing a similar colour
vision defect to that known as protanopia, which is caused by a lack of
long-wave sensitive cone cells in the retina. Further, there are very few
short-wave sensitive cones in the human fovea, so visual acuity in the blue part
of the spectrum is very poor.
Blue is the most dangerous colour to tint vehicle windscreens or even
driver’s sunglasses. If a filter is required, it should be colour neutral for
safety reasons.
Letters : Selective vision
Middlesbrough
The item on “Christmas Filter Specs”
(Feedback, 5 January)
reminded me of Zaphod Beeblebrox’s sunglasses in The Hitch Hiker’s Guide to
the Galaxy. The Ju Jenta 200 Super Chromatic Peril-Sensitive sunglasses were
designed “to help you develop a relaxed attitude to danger”. At the first hint of trouble
they turn totally black “and thus prevent you from seeing anything that might
alarm you”. Is this a patent infringement?
Letters : Build first, ask questions later
Sydney
In his article on the row surrounding the proposed Chalillo dam in Belize,
Fred Pearce describes the frustration of biologists who were brought in to
conduct an environmental impact assessment鈥攐nly to have their
recommendation that the dam should not be built ignored
(22/29 December, p 4).
In Australia, the “don’t start the project” option is seldom considered in
any major development, not just the construction of large dams. Here, the usual
sop to environmental responsibility is an assurance that a “monitoring
programme” will be established. Of course, even if such a programme showed dire
environmental impact, the construction could not be abandoned nor the
infrastructure demolished (quite difficult with large dams).
For example, the environmental impacts of the Snowy Mountains Hydroelectric
Scheme in Australia have been recognised for several decades, but only recently
have attempts been made to ameliorate these impacts. Surely a new international
standard for environmental impact assessment is required.