Frontier Bushcraft Instructor James Bath demonstrating the use of a parabolic mirror. Photo: Duane Yates.
You may have heard of the so-called 'Walkie-Talkie' skyscraper.
The £200 million building is situated at 20 Fenchurch Street in the City of London.
The 37-storey glass-covered tower hit national and international news headlines due to it creating a beam of light that "melted cars".
In a late summer spell of clear skies and warm sunshine, the curved surface of the building was found to be reflecting sunlight into a concentrated spot on the street below.
This phenomenon is similar to that of focusing sunlight with a magnifying glass - a concept that many people are familiar with.
The effect at work here, though, is that of a parabolic reflector.
The reflective properties of a parabolic mirror have been understood since at least the 3rd Century BC, when the Greek mathematician Diocles wrote about them in his book On Burning Mirrors.
Unfortunately the architects of 20 Fenchurch Street are not up on their classical geometry.
Nor do they seem to be versed in basic survival skills.
Focusing solar energy is an important method of ignition when it comes to fire-lighting.
Indeed, using a parabolic mirror (or a magnifying glass) is a very reliable - and quick - method of gaining ignition in sunny climes where dry tinder is available. In Africa a classic tinder for this is a piece of dried elephant dung. In the photo above the tinder is a dried rabbit dropping.
Jumping back to the City of London, the beam from 20 Fenchurch Street was sufficiently powerful to cause damage to at least one parked car and start a doormat in a shop on Eastcheap smouldering. A resourceful City AM reporter even used the concentrated heat emanating from the building, which has been quickly re-dubbed the "Walkie Scorchie", to fry an egg.
On the hottest September day in 7 years, the beam of light - up to six times brighter than direct sunlight - was measured at a temperature of 110 degrees Celsius (230 Fahrenheit).
As mentioned in the above video, the property developers quickly produced a statement, which included "The phenomenon is caused by the current elevation of the sun in the sky. It currently lasts for approximately two hours per day, with initial modelling suggesting that it will be present for approximately 2-3 weeks."
Hmmm, that's alright then, it'll go away in a couple of weeks. Very reassuring.
I'm assuming, however, they've realised the Sun has a very predictable cycle and it will pass through this range of elevations again for the same amount of time next year?
In fact, they don't even have to wait that long. Given the symmetry of the annual cycle around the Solstices, City workers should expect to be able to fry eggs in Eastcheap every April too.
Let us know what you think in the comments below. Have you used parabolic mirrors to light fires? Or have you cooked an egg in an unusual way or location? We'd love to know...
Paul Kirtley is owner and Chief Instructor of Frontier Bushcraft. He has had a lifelong passion for the great outdoors and gains great satisfaction from helping others enjoy it too. Paul writes the UK's leading bushcraft blog as well as for various publications including Bushcraft and Survival Skills Magazine.