Has anyone here read it? Is it worth buying??

Has anyone here read it? Is it worth buying??

I have posted this capsule review here befo

| * London Under London: A Subterranean Guide, by Richard Trench(!!)
| and Ellis Hillman(!), 2nd edition, pub.1993 John Murray, P240mM,
| ISBN 0-7195-5288-5.
|
| This covers the entire range of subterranea in London: lost rivers,
| water mains, hydraulic power mains, underground railways, you name it.
| It should therefore be of great interest to you -- but unfortunately,
| in those areas where I already know something what it's talking about,
| I can say that it's riddled with errors.
|
| The worst single sentence is probably this, in the section on electric
| power: it contains at least 4 clear errors and probably more, depending
| on how you count!
|
| ! High voltages generate immense heat, known as superconductivity and
| ! caused by the resistance set up within the cable by the alternation
| ! of the current -- particularly if the cables are laid underground.

On the other hand, there aren't all so many books covering the subject
that you can just go out and find a better one. So read it if you like,
just be aware you can't trust it on details.
--
Mark Brader "You can stop laughing now.
Toronto Well, maybe you *can't*, but you *may*."
-- Rick Burger

My text in this article is in the public domain.

"Mark Brader" wrote in message
...
Has anyone here read it? Is it worth buying??

I have posted this capsule review here befo

| * London Under London: A Subterranean Guide, by Richard Trench(!!)
| and Ellis Hillman(!), 2nd edition, pub.1993 John Murray, P240mM,
| ISBN 0-7195-5288-5.

| The worst single sentence is probably this, in the section on electric
| power: it contains at least 4 clear errors and probably more, depending
| on how you count!
|
| ! High voltages generate immense heat, known as superconductivity and
| ! caused by the resistance set up within the cable by the alternation
| ! of the current -- particularly if the cables are laid underground.

Ha ha! Let's count the errors:

- it's the power loss (I-squared R) that generates the heat, so it's the
fact that high currents are being passed rather than the high voltage
applied which causes it

- superconductivity occurs are very low temperatures (approaching 0 kelvin)
not at very high temperatures - this error is a classic

- any "resistance" that is dependent on the fact that it's AC rather then DC
is impedance, not resistance; the heating is actually a simple I-squared R
and would be the same for AC and DC - the impedence of a straight piece of
wire would be negligible.

- no mention of the skin effect whereby AC flows only in the outer "skin" of
the wire rather then throughout the whole cross-section - I'm not sure how
significant this is at only 50 Hz

However its assertion that the problem with heating is worse when the cables
are underground is correct - firstly because the heat is insulated by the
ground so the temperature will be higher, and secondly because higher
temperatures will cause greater resistance and so more resistive heating.

In article m, Martin
Underwood writes
- superconductivity occurs are very low temperatures (approaching 0 kelvin)
not at very high temperatures - this error is a classic

Not quite, Lord Copper.

Superconductivity occurs when there is effectively[*] zero resistance
to electron flow. Ways that this can happen [+] include a half-empty
energy level with Bose-Einstein statistics and a regular progression of
completely filled energy levels with Fermi-Dirac statistics (these being
responsible for He4 and He3 superconductivity respectively). There may
well be other mechanisms.

It so happens that all known cases of superconductivity occur at
extremely low temperatures (under 10K) or very low temperatures (perhaps
150K, I forget), but there is no theoretical reason why it couldn't
occur at room temperature or even at 400K (123 degrees C) or above.
[*] Not "effectively" as in "almost", but "effectively" as in "as if it
was". I have a vague memory that there's actually some resistance in one
sense, but other effects exactly balance it. BICBW.

[+] This is based on my memory of various bits of reading on the topic.
I'm happy to accept correction from professional quantum mechanics.

--
Clive D.W. Feather, writing for himself | Home:
Tel: +44 20 8371 1138 (work) | Web: http://www.davros.org
Fax: +44 870 051 9937 | Work:
Written on my laptop; please observe the Reply-To address

ronnie biggs writes
Has anyone here read it?* Is it worth buying??

Yes, I have it. I found it a fascinating book - it's surprising just
how much is under there.

--
Dave