Letter
Some misleading information on the relative safety of hydrogen and other
fuels appeared in your feature. It is really very difficult to ignite a mixture
of petrol or gasoline vapour and air. At most ratios these two gases will not
ignite. A near-empty fuel tank in a car contains a considerable quantity of
oxygen, and no amount of sparking will cause ignition. When a mixture of petrol
vapour and air burns, it does so relatively slowly, so that an explosion hardly
ever occurs.
But most ratios of hydrogen and air can be ignited with a spark. The rate of
burning is extremely high, as well, so an explosion often results.
The claim that to work as a fuel, hydrogen requires more oxygen than
gasoline, assumes complete combustion. This is true, but there’s more to the
story. Assuming that gasoline is octane, 1 tonne of it requires about 3.5 tonnes
of oxygen to combust. Compare this with the 8 tonnes of oxygen needed to combust
1 tonne of hydrogen. However, if you accompany that 1 tonne of hydrogen with 3.5
tonnes of oxygen and a spark, the resulting explosion will destroy a
considerable amount of property. Anybody unfortunate enough to be in the
vicinity will not survive to reflect that most of the hydrogen remains
unconverted to water vapour.
I have survived one or two very minor mishaps with hydrogen. It is very
dangerous stuff indeed.
Waterworld
The excellent article on Bill Phillips’s hydraulic model of the national economy
(9 December 2000, p 46)
raises the possibility of using models
incorporating tanks, plumbing and water to help clarify aspects of globalisation
for both pro and anti lobbies in that debate.
The implications of globalisation have never been effectively explored in
simulations, as far as I know. Yet the consequences of removing buffering
devices from other systems鈥攆looding, avalanches, spread of disease (BSE),
regional financial crises and flight of capital, movement of peoples, and so
on鈥攊s all too evident. Maybe the World Bank should launch a plumbing
division.
Change the script
If you’re worried about viruses spreading via HTML in e-mail messages
(9 December 2000, p 14),
rest assured: they don’t. HTML itself is harmless, as
other HTML-enabled e-mail clients such as Eudora prove.
What makes the virus potentially risky in Microsoft Outlook is that it
executes the scripting code that can be included with the HTML headers. This
code is not part of HTML itself, and scripting capability is totally unnecessary
for rendering HTML. One wonders why Outlook included the code in the first
place.
So the solution is far simpler than the fancy scanning software that Barry
Fox says is needed: just switch to an e-mail client that doesn’t enable
scripts.
Fuelling debate
In “Kicking the habit”, your feature on the hydrogen economy
(25 November 2000, p 34),
you fail to answer a fundamental question: can it be guaranteed
that any hydrogen-fuelled car parked in a garage is totally leak-free?
It’s a vital concern. The gas is utterly odourless, but explosive when mixed
with air in any proportion from 5 to 95 per cent. Ask anyone who has used liquid
hydrogen in their laboratory.
Not so hot
Your editorial on the discharges of technetium-99 from Sellafield
(9 December 2000, p 3)
raises important issues of policy on environmental protection, which
are of concern not only to the nuclear industry but also to many other
industries vital to Britain’s prosperity.
It is true that treating stored liquid wastes at Sellafield to remove
plutonium and other radioactive species before discharge into the sea has
increased the discharge of technetium, since technetium is not removed by the
process. But the environmental impact of this discharged technetium is very
small. People living nearest to Sellafield, who are assumed to consume large
quantities of local seafood (about ten times the average), receive a dose of
radiation from the technetium that is only about 1 per cent of natural
background radiation鈥攐r, to put it another way, less than 10 per cent of
the dose of radioactivity that naturally occurs in the seafood itself. For
people in Ireland who consume large amounts of seafood, the dose received from
all the Sellafield discharges was reported by the Radiological Institute of
Ireland in 1997 to be less than 0.1 per cent of natural background
radiation.
It is clear, then, that reducing technetium discharges further would have
very little beneficial effect in Britain and no discernible effect in other
countries, including Ireland and Norway, but it would increase the risk to the
workforce as well as costs.
According to current policy, the environmental control needed to protect
humans will ensure that other species are not put at risk, but it is generally
agreed that the environment merits protection in its own right. However,
research on marine organisms leads to the conclusion that there would be no
significant effects even at dose rates 500 times those received by lobsters
living close to Sellafield.
The imposition of arbitrary regulations on discharges from industrial plants
that are based on emotion rather than reason and that cannot be justified in
terms of costs and benefits would create a precedent for British industry as a
whole. There is a danger that industry could become driven by an approach
divorced from sound science. This could lead, in turn, to wasting national
resources that could be better devoted to areas of greater need. Nor would it
allow national priorities for environmental protection to be properly set, and
it might have a damaging effect on many industries.
Letter
I was successfully fooled by the four tests designed to demonstrate the power
of the illusions the mind can create. I think, though, that it may be an element
of confusion rather than illusion that fooled me.
All the tests start with the statement, “There is a pin and/or a bolt on the
table, or else there is a bolt and a nail on the table.” The “or else” is
supposed to be read as “exclusive or” or just XOR for short.
Here’s the statement, rewritten without changing the meaning: (There is a pin
and/or a bolt on the table) XOR (there is a bolt and a nail on the table). If
the left side of the statement is true, the right side must be false鈥攁nd
vice versa. The left side contains these two possibilities: (There is a pin and
a bolt on the table) and (There is a pin or a bolt on the table). The latter
contains two possibilities: (There is a pin on the table) and (There is a bolt
on the table). All these possibilities are exclusive to the right side of the
statement, and the last one leads to an intrinsic contradiction: (There is a
bolt on the table) XOR (there is a bolt and a nail on the table). This
possibility forces the “or else” to be read as “or”鈥攊n which case this
very interesting article’s test-analysis will contain a potential for
adjustments.
Letter
Several readers have suggested that the mental illusions reported in “Fooled
again” might be attributed to interpretations of the wording of the questions,
rather than an inability to deal with falsity. Philip Johnson-Laird, who carried
out the research, believes he has eliminated this possibility. He asked subjects
to explain their thought processes out loud while completing the tasks and
corrected any misinterpretations. The illusions, he says, remained just as
蝉迟谤辞苍驳鈥抬诲
The perfect bait
The serious decline in cod stocks
(16 December 2000, p 21)
means we’re looking closely at fish farming again. But it’s a costly option, and
fishmeal鈥攖raditionally a major ingredient in fish food鈥攚ill
inevitably decline in quality and quantity as stocks become scarcer.
Enter the earthworm. Earthworms are nutritionally superior to fishmeal and
are now produced cheaply and in large amounts. And they have other benefits. The
worms consume waste vegetable material such as carrots discarded from markets
and even shredded cardboard, so the problems of organic waste disposal are
solved. They are also raised on farms in special beds isolated from the soil, so
there is no risk of BSE.
In fact, the fish themselves could be raised on land, in recirculation
systems鈥攑reventing the kind of environmental damage that farming salmon,
halibut or seabass in sea cages is now known to cause. It could all add up to a
real future for fish as food.
Fool the mind
A couple of points strike me about the article on logical breakdown
(9 December 2000, p 24).
Mental models that include falsity are difficult to build because they mix
the concrete and the symbolic. Take the old example offered by thinkers of
various kinds down the ages: “Don’t think of an elephant.” It’s almost
impossible not to. We find ourselves briefly thinking of the elephant, even if
we then go on to blank our minds or to think of something else. And one way that
many people handle the situation is to think of the elephant, but superimpose
some idea of negation, such as a “no entry” sign. The elephant is an image of
something concrete, whereas we handle negation symbolically.
Building a mental model that includes falsity means we must do one of two
things. First, we could superimpose some symbol of falsity or negation onto our
images of concrete things. But in this case it is probably harder to extract the
truth, since we have to juggle with the concrete and the symbolic, perhaps by
switching backwards and forwards between the two鈥攁 potentially confusing
feat.
Secondly, we could hold two models in mind simultaneously: a model of what is
asserted as true and a model of something else, which could be of anything as
long as it isn’t what is asserted as true (for example, in the elephant example
above, it could be a monkey). The obvious drawback to this solution is that the
“anything else” doesn’t necessarily relate in any real way to the original
assertion.
Either of these two methods of problem-solving requires us to expend far more
energy than if we were simply working with images of concrete things. My
personal feeling is that those people who are good at solving problems involving
falsity are those people who can translate the whole thing into some form of
symbolic logic so that they are no longer working in the realm of the concrete.
I think that the explanations that Brooks gives for his later examples
demonstrate this nicely.