Letters: Chilling thought
Andy Coghlan (Technology, 31 July) comments on the low chance that
any of the people frozen before death in the hope of preservation for future
survival, can be revived successfully. Such a chilling thought is only half
as bad when we remember that cryonicists only freeze the already dead.
Amber Hetzler Beilstein, Germany
Letters: Rail gun thing
This rail gun thing (Technology, 17 July) reminded me of long ago in
Cambridge, late 1939 or early 1940, when a chap took over my research room
and built a small rail gun with rails a metre or so long, and firing pellets
of maybe 50 grams. I was annoyed because the pellets kept taking chips
off my nice panelled door.
He finally had a display for some top brass, which I attended, on a
common near Cambridge, with a bigger model and a projectile of perhaps 200
grams and a van full of capacitors. We stood respectfully well back, and,
on firing, the shot flew all of 7 metres, but the driving band-cum-armature
flew about 100 metres. I never saw him or heard of him again.
In 1945, in mid-July, shortly after V-E Day, I joined a group of three
or four others on a search in Germany for secret weapons. We landed on a
temporary air strip at Frankfurt and drove in an uncomfortable American
ammo lorry to Munich and on into the Bavarian Highlands. In a remote big
country house we found a small group with a larger rail gun with a projectile
of half a kilo or so, rails about 4 metres long, plus a large van filled
with several cubic metres of capacitors and a generator. It had never worked
because the armature always welded itself to the rails on passage of the
pulse of a million amps or so. The boss probably had friends in high places
and was put there to keep him out of the way.
Silly ideas often don’t die, they just fade for a few decades and then
come back as something new and wonderful. So we have the Kirkcudbright rail
gun firing a solid tungsten shot, not a shell, and with a muzzle velocity
of, say, Mach 10.
Such a gun certainly has problems. The sliding armature attached to
the shot and bridging the rails must give a sliding contact both of low
friction and low electrical contact resistance. Difficult. I doubt if the
shot will be in flight long enough for air resistance to melt it, but it
must have fins to give it stable flight since it is nonrotating, and these
could easily melt.
A big problem is the huge volume of capacitors required for energy storage,
and also the electrical generator. I doubt if it will ever be possible
to squeeze it into a tank.
From my experience, I would not put any money on the gun’s success,
but it will undoubtedly keep the team of scientists and engineers in hot
dinners for some years.
J. F. Allen University of St Andrews
Letters: Cannabis control
As someone who has been using cannabis illicitly for two years to control
multiple sclerosis, I am very pleased to read that research into its therapeutic
properties is yielding results (‘Cannabis: the brain’s other supplier’,
31 July). I and several other patients use cannabis as, after taking different
prescription drugs for many years, we have found there is no other medication
available which is as safe and effective for reducing spasticity, nausea
and loss of balance. Six months ago we formed a British branch of the American
Alliance for Cannabis Therapeutics, and already we have dealt with dozens
of enquiries from patients in this country desperate for some alternative
to their current treatment. If the researchers in your article are hampered
by the stigma of working with a ‘drug of abuse’, we patients also find it
disheartening and confusing when we constantly come across ignorance and
suspicion from the medical profession.
Clare Hodges Alliance for Cannabis Therapeutics Leeds
Letters: On being dense
Few dispute the relationship between city density and travel or car
use, but figures cited in Mick Hamer’s ‘City planners against global warming’
(24 July) hide ruses that hopefully readers have already spotted.
In the graph of urban density versus petrol consumption (from Peter
Newman), readers get suspicious finding that Toronto has a higher density
than New York, as does even Los Angeles. The problem is that no one knows
how the lines are drawn around ‘cities’, so we don’t know what population
(or driving) is included.
Newman and colleagues have not measured ‘petrol consumption’ per capita,
but only inferred it from very sketchy data about cars and traffic around
cities. As we found in our own studies, virtually no one knows the petrol
consumption of citizens in the American or European cities shown in the
graph; the best that is known is sales within a certain boundary, as evidenced
by tax receipts. These are only distantly related to how much those who
live there travel, ignoring traffic through the city, particularly for the
low-density towns in the US. Houston is full of filling stations, but try
to find one in downtown New York, Stockholm, or Paris. Hence the vertical
axis of this graph does not measure car fuel consumption related to the
mobility of people living in the city in question.
Surveys show that people who live in the city centre own fewer cars
and travel somewhat less than those living elsewhere, a demographic and
income effect (higher car insurance and maintenance costs) not a density
effect alone. Those that do own cars drive them less and walk more, to be
sure. Those living in suburbs (which may or may not be counted fairly in
the Newman data) drive more. The lower fuel consumption apparent from comparing
Europe and the US results more from the low auto ownership in actual cities
in Europe (as opposed to the suburbs), the lack of American-style gas guzzlers,
and lower driving per car in Europe, than from some magic of density alone.
In the final analysis, population density does influence car use, but
it also has a large effect on virtually every other feature of everyday
living, both positive and negative. While it would be nice to control sprawl
of our American cities, one should look beyond the distortions of the simplistic
figures of the Newman study to a better representation of the costs and
benefits of living differently.
Lee Schipper Lawrence Berkeley Laboratory California
Letters: Pleasantly baffled
I sympathise with Paula Beesley in lamenting the loss of Fermat’s last
theorem from the list of great unsolved mathematical problems (Letters,
31 July). I am delighted, however, to be able to introduce her to an even
more pleasing and still unsolved problem.
Goldbach’s conjecture asserts that every even number is the sum of two
primes. This simple conjecture continues to resist proof, although Chen
Jing-run came close in 1973 with a proof that every (sufficiently large)
even number is the sum of a prime and a number that is either a prime or
the product of two primes.
The reason I find Goldbach’s conjecture more aesthetically appealing
than Fermat’s theorem (or the four colour problem) is its extreme simplicity.
Note in particular that, unlike Fermat’s theorem, Goldbach’s conjecture
(if true!) can be proved for all integers less than some arbitrary maximum
by means of finite search.
I hope that this news will help return Beesley to a state of pleasant
bafflement.
Rupert Ward Oxford
Letters: Commuter challenge
The anomalous behaviour of the digital clock on Godalming Station (Letters,
3 and 24 July) provides an interesting challenge in deductive logic. Leaving
spurious metaphysics aside, my companions and I permitted ourselves the
duration of the journey from Malet Street to Egham to determine the simplest
mechanistic explanation for the appearance of an ‘eight’ instead of a ‘zero’.
For example, could it be the result of a simple short-circuit between any
two of the seven segments of the display? It appears not.
This substitution requires the unique condition that the centre horizontal
segment be activated when it, alone, should not. Since all the other numbers
display correctly, a truth table quickly demonstrated that there is no other
segment to which a direct, interconnection could be made. A similar analysis
shows that there are just three one-way, diode-like links which could account
for the observation. Can any logician tell us please, what is the simplest
mechanistic explanation?
Daisy Felix Academic Commuters’ Study Group London
Letters: Blameless farmers
You may be right to say that the European Commission’s directive on
drinking water purity was tough (Comment, 24 July), but it is sad that you
fall for the popular myth that current farming fertiliser practices have
much to do with nitrate levels in our water supply, or that changes will
significantly improve matters.
As you could readily discover from the 150 years’ investigation into
nitrogen in agriculture by the world’s leading soil chemistry research station
at Rothamsted, water derived from soil which has had no artificial nitrogen
applied since the middle of the last century still contains nitrates. Some
40 kilograms of it seeps out from each hectare, whether cultivated or not.
Much of the current concern over farm-derived nitrate levels is now
recognised to be attributable to the orders issued during the last war compelling
farmers to plough up old grassland, the nitrogenous derivatives from which
have taken best part of half a century to emerge in our rivers – without
evidence of harm to anyone.
In recent years a combination of new slow-release fertilisers, improved
uptake ratios, and more sophisticated timing of applications, together with
a price squeeze, has significantly reduced nitrate levels attributable to
the application of artificial fertilisers.
Montague Keen Sudbury, Suffolk