The Dangerous Book for Boys. Conn Iggulden
Чтение книги онлайн.
Читать онлайн книгу The Dangerous Book for Boys - Conn Iggulden страница 7
Название: The Dangerous Book for Boys
Автор: Conn Iggulden
Издательство: HarperCollins
Жанр: Справочная литература: прочее
isbn: 9780007444403
isbn:
4. WHAT IS LATITUDE AND LONGITUDE?
The Earth is a globe. The system of latitude and longitude is a man-made system for identifying a location anywhere on the surface.
Latitude takes the Equator as a line of zero. If you cut the world in half at that point, you would have a horizontal plate. The centre point of that plate is at ninety degrees to the Poles above and below it.
Latitude is not measured in miles but in the degrees between ninety and zero in both hemispheres. London, for example is at 51° latitude north.The curve representing the ninety-degree change is split into imaginary lines called ‘parallels’ – because they are all parallel to each other and the Equator.
With something as large as the Earth, even a single degree can be unwieldy. For both longitude and latitude, each degree is split into sixty ‘minutes of arc’. Each minute of arc is split into a further sixty ‘seconds of arc’. The symbols for these are:
Degrees: ° Minutes: ’ Seconds: ”
With something as large as a city, the first two numbers would suffice. London would be 51° 32’ N, for example. The location of a particular house would need that third number, as well as a longitude coordinate.
There is an element of luck in the fact that a latitude degree turned out to be almost exactly sixty nautical miles – making a minute of latitude conveniently close to one nautical mile, which is 6,000 feet (1852 metres).
The longitude of London is zero, which brings us neatly into longitude.
Longitude is a series of 360 imaginary lines stretching from Pole to Pole. London is zero and 180 degrees stretch to the west or east.
If the world turns a full circle in a day, that is 360 degrees. 360 divided by 24 = 15 degrees turn every hour. We call the fifteen-degree lines ‘meridians’. (‘Meridian’ means ‘noon’, so there are twenty-four noon points around the planet.)
Now, this is how it worked. On board your ship in the middle of nowhere, you took a noon sighting – that is, took note of the time as the sun passed its highest point in the sky. You could use a sextant and a knowledge of trigonometry to check the angle. If you were at noon and your ship’s clock told you Greenwich was at nine in the morning, you would have travelled three meridian lines east or west – which one depending on your compass and watching the sun rise and set. You would be at longitude +/–45°, in fact.
Having a clock that could keep the accurate time of Greenwich even while being tossed and turned on a ship was obviously crucial for this calculation. John Harrison, a clock maker from Yorkshire, created a timepiece called H4 in 1759 that was finally reliable enough to be used.
All that was left was to choose the Prime Meridian, or zero-degree point of longitude. For some time it looked as if Paris might be a possibility, but trade ships in London took their time from the Greenwich clock at Flamstead House, where a time ball would drop to mark 1 p.m. each day. Ship chronometers were set by it and Greenwich time became the standard. In 1884 a Washington conference of twenty-five nations formalised the arrangement. If you go to Greenwich today, you can stand on a brass line that separates the west from the east.
On the opposite side of the world, the two hemispheres meet at the International Date Line in the Pacific Ocean. It’s called the International Date Line because we’ve all agreed to change the date when we cross it. Otherwise, you could travel west from Greenwich, back to 11 a.m., 10 a.m., 9 a.m., all the way round the planet until you arrived the day before. Obviously this is not possible, and so crossing the line going west would add a day to the date. Complex? Well, yes, a little, but this is the world and the systems we made to control it.
Like latitude, longitude is broken down into a three-figure location of degrees, minutes and seconds. Common practice puts the latitude figures first, but it’s always given away by the North or South letter, so they can’t really be confused. A full six-figure location will look something like these:
| 38° 53’ 23” N, 77° 00’ 27” | W Washington DC |
| 39° 17’ 00” N, 22° 23’ 00” E | Pharsalus, Greece, where Julius Caesar beat Pompey and ended the civil war. |
| 39° 57’ 00” N, 26° 15’ 00” E | Troy |
5. HOW DO YOU TELL THE AGE OF A TREE?
You cut it down and count the rings. For each year of growth, a dark and a light ring of new wood is created. The two bands together are known as the ‘annual ring’. The lighter part is formed in spring and early summer when the wood cells are bigger and have thinner walls which look lighter. In autumn and winter, trees produce smaller cells with thicker walls which look darker. They vary in width depending on growing conditions, so a tree stump can be a climate record for the life of the tree – sometimes even centuries. The age of a tree, therefore, can be told by counting the annual rings.
A BATTERY AT ITS SIMPLEST is a cathode (the positive end), an anode (the negative end) and electrolyte (the bit in the middle). There are quite a few different combinations out there. Electricity is the movement of electrons, tiny negatively charged particles. The anode tends to be made of a substance that gives up electrons easily – like zinc, which gives up two electrons per zinc atom. The cathode tends to be made of substances that accept electrons easily, like copper.
The electrolyte inside can be a liquid, a gel or a paste. All that matters is that it contains positive and negatively charged ions that flow when the anode and cathode are activated. When the Italian physicist Alessandro Volta made the first battery, he used copper for the cathode, zinc for the anode and an electrolyte of blotting paper and sea water. His name gives us the word ‘volt’, as in a 12-volt car battery. If you think of electricity as a water pipe, a volt will be the speed of the water, but it also needs a big hole to flow through – or ‘amps’. You can have enough voltage to make your hair stand on end, but without amps, it won’t do more than cause a tiny spark. A house supply, however, has 240 volts and enough amps to kill you as dead as a doornail.
You will need
Ten two-pence pieces.
Metal СКАЧАТЬ