Best of the rest - Why Can't Elephants Jump?: And 101 Other Tantalising Science Questions - New Scientist

Why Can't Elephants Jump?: And 101 Other Tantalising Science Questions - New Scientist (2010)

Chapter 8. Best of the rest


Net rage

When a thread or topic is started on a user-generated forum on the internet, it isn’t long before one of the contributors makes a seemingly unprovoked attack on a total stranger. What is it about non-face-to-face contact of this kind that makes this more common than it would otherwise be?

John Anderson

Warsaw, Poland

In 1987, psychologists Mary Culnan and Lynne Markus refined the ‘reduced cues theory’ to explain potentially abusive behaviour online.

They suggested that computer-mediated communication is inferior to face-to-face contact because social cues such as body language, tone, volume and intensity of speech are lacking. An online conversation, therefore, except when a webcam or microphone is used, takes place in what is termed a ‘social vacuum’. The reduced cues that are available to each correspondent can lead to a lack of individual identity (deindividuation), which in turn undermines any social and normative influences.

Overall the lack of these strong influences can lead to forms of uninhibited and atypical behaviour. Behind a computer screen you are usually fairly safe from physical retaliation. This creates a sense of safety and a disguise for participants which is further reinforced by the control individuals can exert over their online identity.

On user-generated forums, for example, you can choose what profile information about yourself is displayed, fabricate that information, and in most cases choose not to disclose it to fellow participants at all. Similarly, in virtual worlds you can take on a name and an avatar which is entirely unlike the real you.

As to the motive behind an unprovoked attack, human beings are undeniably complex creatures: the reasons could range from simply having a bad day at work to wanting the excitement of causing trouble.

Thomas Venus

Nuneaton, Warwickshire, UK

Social interaction depends on innate and acquired attitudes, including the urge to be imposing, formidable or dominant. Contrary factors, such as fear, upbringing, affection or social pressures, tend to dampen down extremes of behaviour and prevent loss of control.

A healthy balance of all these structures one’s behaviour in a socially desirable manner. Remove this feedback, and misfits, habitual victims of bullying or products of unhappy backgrounds revel in the freedom to indulge in bullying or sadism that has driven sensitive victims to suicide.

More sensible recipients of this kind of correspondence simply wipe off such nuisances in their ‘kill’ lists or otherwise ‘kill them with silence’, as the Japanese wisely put it.

However, people who indulge in abuse and bullying are widespread on internet forums, where they cannot be touched.

Other expressions of perceived immunity include football hooliganism in large crowds, and car drivers who feel safe insulting or threatening others. George Orwell characterised such impulses as ‘the irresponsible violence of the powerless’.

Similar behaviour is common among animals, most familiarly lapdogs in vehicles, or safe behind high fences. They pose and threaten like monsters, but then panic abjectly if their protection fails and someone calls their bluff.

Jon Richfield

Somerset West, South Africa

What a stupid question, you total and utter… LOL!

Fake Name

By email, no address supplied


Touchy feely

In Olympic swimming events, the winner is the first person to touch a pressure-sensitive wall pad at the end of the pool. How does this pad know that a person has touched it rather than just registering the pressure of splashing water? If a swimmer just brushed it, would it fail to register their finish? I know that in the men’s 100-metre butterfly event in the 2010 Olympics in Beijing, the equipment was called into question when Michael Phelps of the US won his seventh gold medal of the games. How did officials know it had operated successfully? And finally, it’s easy to judge the victor in a race taking place out of water - such as running - because a sensor beam can scan the finish line. But in the pool how can they ensure that all the wall pads are exactly in line at both ends of the pool? Are they aligned before water is added to the pool and, if so, how?

Kelly Clitheroe

Grimsby, Lincolnshire, UK

At the end of each lane there is a touch pad 90 centimetres high, 240 cm wide and 1 cm thick. Touching the pad stops the clock. Omega, the manufacturer of the touch pads used during the 2008 Olympics in Beijing, claimed that the pads react to the slightest touch from a swimmer’s hand, but not to the splashing of water.

However, after the argument around Michael Phelps’s victory over Milorad Cavic in the 100 metres butterfly final at the games, later verified by digital images, it was revealed that a pressure of approximately 3 kilograms per square centimetre must be applied to the pad to activate it and stop the clock. Therefore, it can be said that the victor is the person who touches the pad with enough pressure and not necessarily the one who touches the pad first.

Joanna Jastrzebska

North Shields, Tyne and Wear, UK

The pressure pad’s tolerances are supposed to require a swimmer’s touch before it will trigger a response. A pulse of water would have to come from a high-power nozzle to apply enough pressure to trigger the pad.

A swimmer approaching the end of a race cannot push a narrow enough or strong enough stream of water to trigger the pad. However, brushing the pad lightly may also not trigger it and so these days timing officials check overhead, high-speed cameras - like those used in track races - if the pad is just brushed or they are uncertain of the winner for any reason.

Adrian Skinner

Bournemouth, Dorset, UK

The pads are screw-fixed to the poolside along their top edge and in close contact with the poolside behind. The swimmer’s positive and forcible pressure on the pad must close any gap between the pad and the poolside, or it may not register.

You have to hit the pad quite firmly to register, either at the turn or at the finish. Just occasionally the pad does indeed fail to register, either through poor swimmer contact or pad malfunction. This is why there are back-up timekeepers on each lane - both human and electronic - in order to verify a result. If a world or championship record is at stake, there must be at least three timekeepers present, and one of them has to be electronic.

The final published time may have to be scrutinised by the referee if there has been a mechanical problem; sometimes a compromise or average time may be recorded at the referee’s discretion. Sometimes the record has to be disallowed if the electronic timing device is in any way compromised.

If a pad should malfunction during the course of a race, it is removed and exchanged between events, which takes about 5 minutes. The new pad is tested by punching it manually while timekeepers in a control room monitor the effect.

In major events, reaction times off the starting blocks are also electronically measured by sensors and displayed instantly on the scoreboard (this identifies false starts). The changeover time is also registered in relays, to show if the outgoing swimmer left the blocks before the incoming swimmer hit the pad. Relay swimmers still in the water while the race continues must take care not to touch any of the pads by mistake when they exit the pool, to avoid confusing the timing systems.

Phil Sears

Amateur Swimming Association club coach

Dorking Swimming Club

Westcott, Surrey, UK


Jump start

A sprint athlete is deemed to have false-started if they react within 0.1 seconds of the starting gun. This seems like a rather arbitrary round figure. What studies have been done to test human reaction times, and is the fastest a person can react to the sound of a gun really exactly 0.1 seconds?

Cathy Jameson

Barrow, Cumbria, UK

The earliest scientific research into human reaction times was undertaken in 1865, by the Dutch physiologist Franciscus Cornelis Donders, best known in his lifetime as an ophthalmologist but who was responsible for pioneering studies in what became known as mental chronometry.

Donders measured response times by applying electric shocks to the right and left feet of his subjects. They responded by pressing, as quickly as they could, an electric telegraph key to indicate which foot had been shocked. In some tests the subjects were warned beforehand which foot was to be tested, in others no prior notice was given. By measuring the difference in reaction times between the two types of test, which he found to be 0.066 seconds, Donders made the first tentative calculation of the speed of a human’s mental responses.

In the example raised by your questioner, where a starting gun is used, the figure established by the International Association of Athletics Federations, 0.1 seconds, is in line with the response time measured by Donders, rounded up to one decimal place. So, yes, that is almost certainly the fastest time an athlete, even after repeated practice, could respond to the starter’s gun. If they react any faster, the clear inference must be that they were launching themselves off the blocks before the gun was fired.

Hadrian Jeffs

Norwich, Norfolk, UK

Many experiments have been carried out on reaction times. A number of these were performed by psychologists attempting to gauge correlations between reaction times and intelligence. Although a small positive correlation was found in this area by Ian Deary, Geoff Der and Graeme Ford of the Universities of Edinburgh and Glasgow, UK, in 2001, the issue is still contentious.

There are three main approaches to measuring reaction time. In the simplest of these, only one stimulus is presented to the subject, who is restricted to only one response. In the second type - called recognition reaction time experiments - several different kinds of stimuli are presented to the subject, who is required to respond to one kind and ignore the others; again there is only one correct response. Finally, in choice reaction time experiments, subjects are required to give different responses to different stimuli: for example, to press one button if a red light appears and another button if a green light appears.

Whichever approach is used, subjects normally perform several trials. The response times are then averaged to compensate for the variability from trial to trial, and so give a more reliable measure.

In the specific case of a starting gun, response times to auditory stimuli have been studied for a long time, and the generally accepted reaction time is approximately 0.16 seconds. However, there is a great amount of variation between individuals, as well as differences in single individuals over time.

Ian Smith

London, UK


Ocker stopper

In Australia, the loud, shrill call of ‘Cooee!’ is often used over long distances in rural and mountainous areas to draw attention to oneself. What is it about this word that makes it more audible over distance and is there a word more suited to drawing attention to myself should I be lost in the outback?

Tom Langford

Brisbane, Queensland, Australia

Plenty of speculation on this one so we’re keeping the file open for a while. Thanks to those who point out that ‘Gooweet’ was devised by Australian Aborigines for gaining long-distance attention, while a few hundred years back ‘hoooooha’ was popular in Sri Lanka - Ed.

A person’s hearing is most sensitive between 1 kilohertz and 4 kilohertz, peaking at about 3 kilohertz. When someone hollers ‘cooee’, the highest part of the call is generally between 1 and 4 kilohertz. So it’s not that the call itself carries better, it’s just that we humans hear better at that pitch.

Nate Dog

By email, no address supplied

The word ‘cooee’ is more audible because it contains two open, long vowels. When pronounced, ‘coo’ opens up your throat allowing it to resonate. When the subsequent ‘ee’ is pronounced your throat closes slightly and the sound resonates loudly in your mouth and nasal cavity.

In contrast, when you say ‘help’, for example, this contains a very short vowel which only sounds in a narrowed throat.

So these ‘big’ vowels allow you to send your voice out louder and larger. As for words that will draw attention to yourself… any swear word with ‘big’ or ‘long’ vowels will do.

Natalie Arad

By email, no address supplied

The ‘c’, or any other explosive consonant, carries poorly and only helps to launch the subsequent vowel sounds. What you need to remember is that there are two very different vowel sounds which are at opposite extremes - one has almost no overtones, while the other is rich in them. Also, each vowel sound is sustained long enough not to be obscured by so-called multipath distortion, when different sounds reach the listener at the same time and thus confuse reception.

Similar considerations are apparent in the International Radiotelephony Spelling Alphabet (under which letters are known as ‘Alpha’, ‘Bravo’, ‘Charlie’, and so on for the purpose of clarity), and related procedural words such as ‘Roger’ and ‘Mayday’, which are chosen to be distinct even if you can only discern the vowel sounds. In fact, evidence shows that people use similar sounds when choosing a name for a dog; two distinct vowel sounds are best when calling it from a distance.

Ron Davis

By email, no address supplied

Australians may use this call to signal from afar, but Austrians yodel. In fact, ‘cooee’ resembles ‘yodel(odel)ayitee’ in that it contains broken, not continuous, sounds and also ends in ‘ee’.

Comparative trials seem to bear out the use of these sounds, even taking into consideration climatic factors such as mist, rain and snow, and terrain such as bare rock against vegetation.

P. G. Urben

Kenilworth, Warwickshire, UK


You cannot be serious

How accurate can the automated tennis line-judging system called Hawk-Eye be? Surely for the level of accuracy it seems to offer, it would need far more cameras than appear to be present at major tennis tournaments. Yet everybody happily accepts its rulings. How does it work?

Franco Pallatini

New York, US

Briton Paul Hawkins created and named Hawk-Eye, a system which combined the expertise he gained for his PhD in artificial intelligence with his passion for sport, particularly cricket.

In cricket, a batsman can be given out ‘leg before wicket’. This ruling is applied when the umpire believes the ball would have gone on to hit the stumps had the batsman’s leg not been in the way. In this situation Hawk-Eye can be used to predict the ball’s trajectory and is arguably more reliable than an umpire.

Despite being invented with cricket in mind, it was tennis that was receptive to the technology much earlier, perhaps thanks to TV replays showing that umpiring mistakes contributed to the defeat of Serena Williams by Jennifer Capriati in the 2004 US Open quarter-finals. Hawk-Eye provides an instant replay of crucial shots and has also proved an excellent tool for analysing the strategy and performance of players.

For tennis, it relies upon a maximum of six cameras to provide data for sophisticated triangulation. The position of the ball is tracked via a succession of stills from each camera. Within a virtual recreation of the tennis court, a ray can be drawn from each camera through the centre of the ball. The intersection of these rays provides the position of the ball in three dimensions and, with the passage of each frame, its velocity. This can be used to calculate the contact area of the ball with the court, taking into account the distortion of the ball after it is hit. Hawk-Eye also captures any skidding of the ball on the court, which can deceive the eye into believing a ball is out.

Mike Follows

Willenhall, West Midlands, UK


Call me for dinner

I placed my mobile phone in my microwave oven, closed the door and then called it from a landline. I expected the oven to shield it from the incoming microwaves, but to my surprise the phone rang. Does this mean the oven is tuned or that it is leaking?

Tam Anderson

Kirkcaldy, Fife, UK

Mobile phones and microwave ovens are designed to operate efficiently within a narrow band of radio frequencies. The microwave oven is tuned to 2,450 megahertz, which is 650 MHz higher than the highest band a European dual-band mobile phone can use and 550 MHz higher than an American phone. You might say that the oven and the phone are not on the same channel. The oven is designed to keep in all the energy it produces, in order to cook food. It does this well, thanks in part to regulations limiting leakage of the 2,450 MHz microwave energy that it uses. But at other frequencies - say the 900 MHz, 1,800 MHz or 1,900 MHz used by mobile phones, but for which the oven shielding is not designed - it might well leak energy in or out, which would permit a mobile phone to work from inside the oven.

Michael Brady

Asker, Norway

A friend of mine placed a mobile phone in the microwave and turned the oven on. This is not advisable. Because I am an electronic engineer, my friend then asked me if the phone could be repaired. It could not.

By email, no name or address supplied

I have made some interesting observations about microwave ovens.

In Alberta it is legal to drive with a microwave detector in the car. This, the manufacturers of the detectors tell us, is for our own safety, because the instruments alert us to the shower of microwave radiation which is emitted by emergency vehicles speeding up the freeway in order to save property and lives.

Perhaps of more interest to many owners of these delicate scientific instruments is that they can detect the radiation emitted by police vehicles intent on reducing the bank balances of speeding citizens. Out of concern for my safety, I carry one of these machines in my 260 horsepower automobile, and guess what? Every time I pass a supermarket which uses microwave ovens, the microwave detector goes off - about 200 metres away, in fact.

Jamil Azad

Calgary, Alberta, Canada

The answer lies in the sensitivity and different tuning of your microwave detector and the shielding of the ovens. The ovens will leak some radiation across the spectrum - which you can pick up - but will not normally leak enough high-energy microwaves to make the ovens dangerous - Ed.


Water substitutes

Is water the ideal liquid in which to swim? Assuming there are no ill effects to your health, would a different liquid that was either denser and more viscous, or had some other property, enable one to swim faster or with less effort?

Robert Laing

London, UK

The speed of a body in fluid is limited by the sum of three factors. The viscous drag is the friction of the fluid against the wetted surface. The form or pressure drag is the force created by the pressure difference between the front and the rear of the body. Finally, there is the wave-making drag, which is the energy wasted in making waves on the surface of the water.

I would suggest two strategies to achieve a higher speed for a given power. Swim totally submerged in a liquid with a lower viscosity and lower density than water, such as acetone, methanol or ether. The lower viscosity would cause less friction and reduce pressure drag, which is proportional to the density of the fluid, cross-sectional area of the swimmer and square of their velocity. Swimming below the surface would totally eliminate the wave-making drag. This is what submarines do to achieve high speeds.

The alternative is to swim on a liquid that has a much higher density than water but low viscosity. Mercury, which has a density 13.6 times that of water, would be ideal.

Archimedes’ principle would ensure that just a small part of the body would be submerged, so the wetted surface and the viscous drag would be very small. The pressure drag would be about the same because while the cross-sectional area of the immersed part of the body would be reduced, the density of mercury is greater. The wave-making drag would remain. And of course you would have to invent a completely new style of swimming, probably something like paddling.

Radko Istenic

Ljubljana, Slovenia

Mercury has to be the best liquid in which swimmers can enhance their performance. A swimmer weighing 90 kilograms whose back has a surface area of 3,000 square centimetres could do a modified backstroke with their torso displacing less than one inch of the mercury.

The swimmer could keep all of their limbs out of the liquid and use vigorous heel kicks into the mercury as an effective means of propelling themselves forward.

Mercury does not wet skin and the sharp shape of its meniscus would further reduce the drag. With less than an inch of immersion, the swimmer’s body would virtually ‘hydrargyro-plane’ across the smooth surface.

The swimmer could use hand strokes for further power and steering, but the technique would require experimentation as limb immersion could slow things down.

In a ceramic-fibre bodysuit a swimmer could do even better in a pool of molten gold, platinum or uranium, displacing barely half an inch of liquid - before frying when the thermal insulation of the suit failed.

David Emanuel

Tulsa, Arizona, US


Freeze frames

I spent time in the Scottish hills last winter and on a couple of occasions I had cause to clean my glasses in a stream that originated from melting snow, effectively at 0 °C. The water cooled the glass and its metal frame to such an extent that both lenses fell out. But how could this happen when, if I remember my school physics correctly, metal should contract more than optical glass because of a higher coefficient of expansion? Obviously this has never happened when I’ve been walking around under normal conditions.

Andy Douse

Drumnadrochit, Invernesshire, UK

We received some very entertaining answers to this question, but we haven’t really nailed it yet. Several people called for more experimentation or wanted to know the coefficients of expansion for optical plastics so that they could be compared with those for metals. Do you know the answer? It’s your big chance to appear in the next book - Ed.

Your correspondent does not say whether he had put the glasses back on when the lenses fell out. If he had, the warmth of his body probably heated the frames more rapidly than the glass. If it happened while he was washing the glasses in the stream, then the rapidly falling temperature might have shrunk the metal frames and squeezed the lenses out.

Doug Grigg

Cannonvale, Queensland, Australia

Unless the questioner’s spectacles were very old, his lenses would be made of plastic not glass. This has a coefficient of expansion many times that of steel.

Alan Hickman

Sleaford, Lincolnshire, UK

Glass lenses could not fall out of a glasses frame as a result of thermal contraction, but most lenses today are polymers. Steel has a linear thermal expansion coefficient of about 2 × 10−5 per °C, while that for polycarbonate is about 7 × 10−5 per °C. On cooling, the lens will contract inside the frame, but the total difference in contraction for 20 °C cooling of a lens 50 millimetres across would only be 0.05 millimetres. Assuming the lenses are properly located in the frame, this should not be sufficient to loosen the lens. I tested this by putting my reading glasses in the freezer - a 40 °C cooling - with no noticeable effect. Some more experiments may reveal why the lenses fell out.

Philip Ward

Sheffield, South Yorkshire, UK



I was having a discussion with my mates about what would happen if you filled a swimming pool with jelly and jumped in. Some of the group believed you would sit happily on the surface. Others, myself included, reckoned you would sink, and risk drowning as the jelly collapsed around you. We wouldn’t want anybody to be harmed, so we don’t recommend experimenting to find out. But is there a theoretical answer to the question?


Bristol, UK

The active ingredient in jelly dessert (or jello) is gelatin, a protein-based gelling product made from collagen.

Gelatin comes in different grades, or Bloom numbers, as measured by the force required to push a plunger into a solution of the stuff to a predetermined depth: the more rigid the sample, the higher the Bloom number. Jelly babies - a popular British sweet shaped like a miniature baby - have a high Bloom number, so there is little danger of drowning in a pool of the mixture used to make them.

The density of jelly is typically 10 per cent higher than water, so a swimmer would float higher in a pool full of jelly than in a pool full of water. Jelly is also more viscous than water, meaning that someone diving into jelly might have difficulty surfacing. However, two researchers from the University of Minnesota, Minneapolis, won the 2005 Ig Nobel prize for chemistry for showing that people could swim just as quickly in water spiked with guar gum, an edible thickening agent, as in ordinary water. The spiked liquid has double the viscosity of water, yet the increased drag is cancelled out by the increase in thrust that swimmers can generate in it.

While we’re on the subject of desserts, custard is interesting, as it becomes much more viscous under pressure. It is possible to walk across a pool full of the stuff, as demonstrated on the UK TV series Brainiac (for a clip of the feat, see

Mike Follows

Willenhall, West Midlands, UK

Jelly is an interesting substance because it behaves as both a solid and a liquid. We did some simple experiments to pin down its behaviour.

We found we could stack five 20-cent coins on top of some jelly before they punctured the surface, meaning the jelly was able to support a pressure of 700 newtons per square metre. This is only around one-tenth of the pressure a person would exert if they tried to sit on a pool of jelly, so presumably such an attempt would fail.

Once the surface broke up, we found the jelly behaved as a very viscous fluid, flowing around a small capsule we pushed into it. From the force required to move the capsule, we estimated the jelly’s viscosity to be around 50 pascal seconds (50 times that of castor oil).

This is so large that a person jumping into a pool of jelly would be slowed dramatically in the first fraction of a second - doing a belly-flop onto jelly would hurt. They would then sink gradually until their buoyancy became neutral, although they would float higher than in water as jelly is a little denser.

Finn Lattimore and Ruth Mills

Canberra, ACT, Australia


Coins of the realm

Photographs of the clock mechanism in Big Ben, the face of the Houses of Parliament in London, show coins on a tray attached to the pendulum being used to tune the oscillation period. Since we all know that mass doesn’t affect the period of a pendulum, why is this done?

Tony Richardson

Ironbridge, Shropshire, UK

Your questioner is correct in saying that the mass of a pendulum does not affect its period. However, the length of the pendulum does, specifically the distance between the pivot and the pendulum’s centre of mass. Adding coins to the pendulum moves the centre of mass slightly, changing the period.

Gareth Shippen

Bromsgrove, Worcestershire, UK

A pendulum swinging under the force of gravity is an example of simple harmonic motion. It is easy to work out that the period is proportional to the square root of its length but independent of the pendulum’s mass.

A clock pendulum is designed to have a period appropriate to the train of gears linking (in most cases) the minute hand with the ‘impulsing escapement’, which converts the oscillations into rotational motion. This period is associated with the length between the pivot and the centre of oscillation, where all the pendulum’s mass is concentrated. Addition of mass above the centre of oscillation will raise this centre, shortening the period. The converse also applies.

In the 1990s I had the pleasure of working for the clockmaking firm Thwaites & Reed, then responsible for Big Ben’s maintenance. The clock’s actual name is the Great Westminster Clock; strictly speaking, ‘Big Ben’ refers to the hour bell. The clock’s pendulum has a 4-second period and its centre of oscillation can be calculated to be about 3.97 metres from the pivot. The addition of a penny to the tray on the pendulum raises the centre of oscillation by 0.0368 mm - enough to cause a gain of 0.4 seconds per day. Removing a penny has the opposite effect.

The pendulum is complex, comprising a steel suspension spring, a steel/zinc/steel temperature-compensating structure, and a cast-iron ‘bob’ attached to the arm, with an adjustable rating nut at the bottom to regulate the swing. The bob swings 3 degrees (about 190 mm) to either side of the vertical. The pendulum’s length, including the spring, is about 4.5 metres and the whole construction weighs 322 kg. It is obvious that it is impractical, even dangerous, to stop the pendulum, make an adjustment to the rating nut and restart it. The disturbance to the pendulum, and to the clock’s timekeeping, would be intolerable.

Edward John Dent and his adopted son Frederick, who built the clock in the 1850s, built their large clocks to run fractionally slow so they could easily be made to tick at the correct rate by adding weights to a top tray. Pennies were used because of their predictable response.

For small swings, a pendulum’s period is independent of the size of its swing, but in Big Ben’s case the pendulum has a large amplitude so this does not hold. Errors of up to 13 seconds a day could occur if the amplitude changed significantly for whatever reason.

That said, I analysed Big Ben’s performance over several years and found it is well able to maintain accuracy of less than 1 second gain or loss per day, more than 95 per cent of the time. Accuracy is maintained by noting and acting upon the difference, if any, between the first strike of the hour bell and the time from the ‘speaking clock’ service provided over the phone. Records show the clock does not appear sensitive to changes in temperature or atmospheric pressure, responding only to the addition or removal of pennies as the clock’s attendants correct random drifts in timekeeping.

So what causes these drifts? Well, there is evidence that the zinc core supporting the bob has been deformed under its load so the position of the bob is lower now than when the clock was built. This has been corrected over the years by increasing the mass on the tray. This stretching means that the pendulum’s temperature compensation is not as good as it once was, but there have been no obvious effects. Any effects arising from changes in atmospheric pressure are likewise too small to observe.

The British Horological Journal (vol. 151, p. 437) describes a pendulum clock designed by horologist Philip Woodward and owned by a Californian, David Walter, that is sensitive to seismic tremors imperceptible to humans, and probably to traffic on a nearby California freeway as well. In a similar spirit, I would speculate that Big Ben can feel the twice-daily ebb and flow of the Thames, as well as vibrations from the tube trains passing underneath, not to mention MPs moving in and out of the chamber of the House of Commons just to the south.

John Warner

Burgess Hill, West Sussex, UK