19.06. How they managed? Bashny.Net

< 240 BC.



Well, that's really like? Archimedes, hit upon the idea how to calculate the volume of irregularly shaped bodies. Or Eratosthenes, who was able to calculate the radius of the Earth. And, second, did not even need pushing in contrast (according to legend) from the first. And that's just the man noticed that in Siena (that is, in Aswan) at the summer solstice on June 19 (well, yes, when it comes to this day), the sun's rays reach the bottom of wells, therefore, the sun shines strongly vertically. Then I calculated that on the same day in Alexandria, the angle of incidence of sunlight is 7, 2 ° (along the length of the shadow set) that is spaced from the sun at the zenith of this magnitude. In a circle of 360 °. Eratosthenes 360 divided by 7, 2 and got 50. Thus, it is found that the distance between Siena and Alexandria still one fiftieth of the circumference of the Earth.
Further calculations - obhohotatsya.
The length of the distance traveled is measured in stages. Caravan of camels usually held about 100 steps per day. Journey from Siena to Alexandria took 50 days. So, to determine the distance between the two cities can be as follows:

100 stages x 50 days = 5000 steps.

Since the distance in 5000 stages equals how Eratosthenes made, one fiftieth of the circumference of the earth, therefore the length of the entire circumference can be calculated as follows:

5000 steps x 50 = 250 000 Stage.

Figured error? Plus-minus Lapot floor, like. But the dude got on exit 39960 km (if you translate the stages, which operated Eratosthenes, as this measure of length "walked" in a certain range). According to Wikipedia, the circumference now considered equal to 40075 kilometers.
It is correlative with acceptable measurement method. Of course, maybe they have a special "measuring" the camels were ...
In "Geography» (Geographika) in 3 books Eratosthenes introduced the first systematic exposition of the scientific geography. He began with a review of what has been achieved Greek science in this area at that time. Eratosthenes knew that Homer was a poet, so he opposed the interpretation of "Iliad" and "Odyssey" as well of geographic information. But he was able to appreciate the information Pytheas. A mathematical and physical geography. He also suggested that if you sail from Gibraltar to the west, you can sail to India (this position Eratosthenes indirectly reached Columbus and told him the idea of ​​his journey). Also supplied his work
geographical map of the world Try at your leisure to build something like that ...
But this is only a small segment of the brain troubled interests. For example, he is the author of the so-called "sieve" Search primes. The very problem of getting prime numbers is a key element in mathematics, it is based on some cryptographic algorithms such as RSA. There are quite a few approaches to this problem, but the most simple - the sieve of Eratosthenes.