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In the hills south of Rome there is an area which, in the
distant past, was volcanic. On the drive from Rocca di Papa to Albano
there is a well-known gentle slope in the road which has an extraordinary property.
If you stop your car, put it into neutral and then slowly
release the brakes, the car will gradually, but perceptibly roll up the hill. I have
observed this phenomenon twice, once as a passenger and once as the driver, both in broad
daylight. Is there any physical explanation?
NICHOLAS HUTTON
London
 | The same effect occurs on the A 719 in Ayrshire, at the Electric
Brae. It has special warning signs because of the likelihood of meeting cars coasting
uphill backwards, as baffled drivers refuse to believe their senses. Coming round the
shoulder of a hill to enter a small, steep valley, the driver sees the road apparently
falling towards the stream. But the road is traversing along the side of the valley,
rather than crossing the stream at right angles and it is actually slightly uphill.
DOUGLAS STEWART
Department of Engineering
University of Aberdeen |
| Near Neepawa in Manitoba, Canada, there is a road called Magnetic
Hill. You drive down a long gentle slope, stop, then release the brake and your car moves
backwards, apparently up the hill. The local residents have finally had to admit that the
hill is not really magnetic, but is actually a very convincing optical illusion produced
by the local topography. No doubt the same applies on the road from Rocca di Papa to
Albano.
PETER BROOKS
Bristol |
| The simplest explanation is an optical illusion, similar to one
experienced by a friend and myself while on a cycling tour of northern Portugal. We were
completely flummoxed to find ourselves having to pedal hard to make progress along a
gently sloping, yet clearly downhill stretch of road. The situation became positively
surreal when a local came towards us also on a bike and apparently uphill, but with his
feet on the handlebars, freewheeling.
JOHN JEFFERIES
Potters Bar
Hertfordshire |
| I have had the same experience twice in the past. I was driving
across western Germany a number of years ago in an old Volkswagen Beetle. The autobahn
along which I was travelling was, for many kilometres, a series of hills like a shallow
sawtooth. My car could only manage about 100 kilometres per hour on the level and the
prospect of driving uphill on this autobahn for five to ten minutes at a time clearly
exposed the power limitations of the engine. The uphill drive was foot-to-the-floor stuff
the whole way.
At a certain point I became aware that I had lost the sense of whether I was travelling
uphill or downhill, because while my eyes told me I was going uphill, the engine revs and
the speed of the car (which had reached 110 km/h) told me I was definitely going downhill.
I later had the same experience in Cornwall. The roads there are almost exclusively up and
down, and at times it is impossible to tell whether your car is level or not
DICK CULLUP
Abu Dhabi
United Arab Emirates |
| I have experienced the same phenomenon at a similar site in
Israel, near Jerusalem, exactly as described. There, the road is cut into the side of the
hill, so that there is a drop on one side and a steep, rocky embankment on the other. The
fact that the car appears to roll up the hill is due to an optical illusion caused by the
relative alignment of the embankment and the road. It is, of course, rolling downhill.
JONINE CORTENS
Brynmill
Swansea |
| I recall seeing a report of a similar occurrence in Australia many
years ago. The road was near the landmark Hanging Rock, which was the setting for a
mystery novel and a more famous film. Given its location, people were, I think, quite
content to enjoy this apparent aberration and assume, or hope for, some unexplained,
attractive force at work. The explanation provided was more mundane, but still curious.
After careful measurement, the road was shown to be sloped, slightly in the opposite
direction to which it seemed.
MARK SETO
St Lucia
Queensland |
| A similar phenomenon can be experienced when driving across the
centre of the island of Cheju Do off the southern coast of South Korea. This is a volcanic
island with the remains of many craters and eroded plugs and the experience is exactly as
the questioner describes.
BRIAN SMITH
East Molesey
Surrey |
| This is almost certainly an optical illusion, like a similar road
at Spook Hill, Lake Wales, Florida. This road seems to slope downwards for a short
distance before climbing a hill, yet cars left in neutral roll backwards, apparently up
and out of the depression. The mystery disappeared when an investigator used a spirit
level to show that the dip is illusory, and the road is in fact uphill all the way. These
observations were published in the autumn 1991 issue of Skeptical Inquirer.
JEREMY HENTY
Cambridge |
| The optical illusion that makes a downhill slope appear to be
uphill is quite common in mountainous districts. It occurs when the true horizon is
obscured by the surrounding hills and more distant hills in the direction of travel are
rather lower than the nearer ones giving one the impression of approaching the summit of a
pass. This effect is enhanced when the valley floor approximates to a plane surface but is
slightly tilted downwards in the direction of travel.
The fact that the questioner only observed this phenomenon in daylight tends to confirm
the above explanation, as the surrounding hills would not be so obvious at night, even
under a full moon. A further visit, accompanied by surveying equipment, would convince
even the sceptical.
RICHARD BURROWS
Tunbridge Wells
Kent |
| I remember from a university surveying course the case of a water
main in the Republic of Ireland, where water was supposed to travel by means of gravity
over a long distance. The drop was carefully calculated but very small. When water was
introduced to the completed main, the engineers were horrified to see it flow uphill, back
towards its source.
The reason turned out to be a local gravity anomaly which meant that gravity in the region
acted not perpendicular to the surface of the geoid, but at a slight angle backwards
towards the water source. The very small anomaly was enough to overcome the even smaller
gradient on the water main. Therefore the water really did flow uphill. I assume a small
pump solved the problem.
OLIVER MOFFATT
Kendal
Cumbria |
| I have experienced an occasion where a major river appears to run
uphill. In the USA, Route 128 leaves Moab, Utah to the east and runs alongside the
Colorado river for several miles. At a certain stretch, the river appears distinctly to be
flowing uphillÑa highly disorienting impression. The rocks of the canyon in which the
river flows are stratified and I suspect that it is the line of their bedding which plays
the trick on the eye.
DAVID COPE
Cambridge |
| I remember seeing a related phenomenon while on holiday in
Cornwall in 1978. But rather than a hill you could roll up, this was, apparently, a
sloping lake. The gradient appeared quite noticeable, although I did not try unpowered
waterskiing on it.
From what I remember, the lake was somewhere near Cape Cornwall, although I have failed to
find it again on subsequent visits to the area. Can any locals let me know where it is?
CHRIS QUINN
Widnes
Cheshire |
| It would be impossible to prove or disprove the antigravity
phenomenon using a spirit level as described. If the antigravity effect can act on a motor
car, it can probably also act on a few millilitres of fluid containing a bubble, causing
the bubble to float downhill instead of uphill. I'm surprised the Skeptical Inquirer fell
for that one.
A STAPLETON
High Wycombe
Buckinghamshire
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