Weighty problem
Question: In 1938, while I was staying at a remote country house, I helped to
wind a suspended weight from the hall up into the roof space. As I recall, its
geared descent generated electricity which lit the sitting room throughout the
evening.
But, according to my calculations, a 1-tonne weight descending from a height
of 10 metres would provide 30 watts of power for no more than 55 minutes.
Can my recollection be correct? And does anyone have any record of such a
device and how it works?
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Answer: The weighted device Mr Hill saw would have been a carburettor of a
type that generated lighting gas from a volatile grade of petrol.
Near where I lived in the 1930s there were at least four of these
installations that were in regular use at large country houses.
John Gibson
Buckingham
Answer: I saw a similar device in a country cottage just outside Reading
early in the 1930s. It compressed a gas and forced it along the piping that
supplied gas mantles for lighting the rooms.
Geoffrey Stanford
Dallas, Texas
Answer: When I was a child in the 1950s, a large country house near where I
lived had an outdoor weight-and-pulley system that was not then in use. I was
told that it was a domestic gas supply which was used for lighting.
The falling weight drove a fan which puffed air over a volatile liquid, and
the resulting vapour was then piped around the house.
Andrew Smith
Bristol
The recollections that are given in these answers are correct. The
pulley-and-weight system did provide light, but not electrical light as the
original questioner thought. The workings of these gas generation systems have
been explained to us by Brian Bowers, formerly a senior curator for lighting
systems at the Science Museum in London. The text and illustration below come
from his book Lengthening the Day: A History of Lighting Technology, which will
be published by Oxford University Press this month.
As far as we know, no working system remains in a country house anywhere,
although we would be very interested to hear if any of our readers knows
otherwise. However, the Science Museum preserves parts of one of the carburettor
machines in its archives鈥擡d
鈥淎nother `home-made鈥� gas used for domestic lighting was prepared from petrol
which had been mechanically vaporized and mixed with air to form an inflammable
gas known both as `air gas鈥� and `petrol gas鈥�. The mixture was explosive if, but
only if, the proportion of petrol was between 2 per cent and 5 per cent. Some
systems used a weaker mixture and others a stronger one鈥攂oth claiming to
be safe. A typical vaporizer had a rotating drum, driven by a falling weight,
which dipped into a container of petrol. As the drum turned, it picked up
droplets of fuel which mixed with a stream of air. If gas were not being drawn
off, the pressure would rise and operate a brake on the mechanism until more gas
was required.
鈥淧etrol gas does not burn with the brilliance of acetylene, and for lighting
it was normally used with mantles. It was also used for cooking and heating. A
railway engineer, giving a general survey of the lighting of railway premises in
1906, included petrol gas as a satisfactory way of producing `a very powerful
light鈥� in situations far from a gas supply and where there was insufficient
demand to justify installing an electric generator.鈥�
Lengthening the Day
Brian Bowers, 1998
Brim swim
Question: My wife swims every day with a small group at the local swimming
pool. Whenever the pool has been filled to the brim, they find swimming much
more difficult and complete far fewer lengths in the allotted time. Why is
this?
Answer: Your questioner should speak to any competitive swimmer to find out
what happens when a pool is filled to a level other than that intended by its
designers.
The pool that his wife uses is presumably one designed with a gutter that is
positioned a short distance below the level of the pool side.
When the pool water is filled level with the lip of this gutter, the waves
that are created by the swimmers (of any speed) will be broken up and
substantially dissipated. This keeps the general surface of the pool flat and
free from large waves. When this effect is particularly noticeable, experienced
swimmers will term the pool 鈥渇ast鈥�.
When the water level is raised or lowered so that the waves hit a reflecting
area of wall, rather than just tumbling into the gutter, they will rebound off
it and add to the general turbulence of the pool, making it a 鈥渟low鈥� pool.
Therefore, an incorrectly filled pool makes swimming significantly harder,
whatever the standard of swimmer, and it will add seconds to a swimmer鈥檚 time,
or cut some lengths off the distance swum by a group.
As well as keeping the water level constant, the manager of the group鈥檚 pool
might be asked to install antiturbulence lane lines which run the length of the
pool, dividing it into segments.
These are used in international and Olympic swimming events to mark the eight
separate racing lanes into which a competition pool is divided. More
importantly, they also break up the wave patterns all over the pool and the
group will be able to swim the same distance even more easily.
Andy Wilson
Solihull, West Midlands
This week鈥檚 question
Into the light: Our local nesting swallows fly very fast from bright sunlight
into the almost total darkness of an outhouse loft.
How do their eyes adapt quickly enough to avoid collisions in the loft?
John Etherington
Haverfordwest, Pembrokeshire