Manaus is the capital city of the state of Amazonas in northern Brazil. The city is situated at about a 10 kilometre distance from the confluence of the Negro and Solimões rivers – two big tributaries of the Amazon river. While these are two names which you must haven’t probably heard of, the place where they meet is a very interesting place.
The first river, Rio Solimões is a water body full of sediments that wash down with it from the Andes mountains. Thanks to the sand, mud and silt that comes washing with it, the river looks muddy, the colour is light brown, nearly. The locals call it the white river.
On the other hand, we have the Negro river (or Rio Negro). It has significantly darker coloured water due to the presence of humic acid from incomplete breakdown of phenol-containing vegetation from sandy clearings. Although the locals call it the black river, it isn’t exactly black. The colour is very similar to a black tea concoction. However, the colour of Rio Negro is very different from Rio Solimões. Here’s how they look from up above.
At the place where they meet, the rivers don’t mix. They leave a fairly clear boundary and flow side by side without mixing for about six kilometres. That happens because of the big difference in their flow speed, density and temperature.
While the river Solimões is a fast flowing (6 km per hour), high density (due to the sediments) and cooler river, the other river flows much slower (one third of the speed of Solimões river), is warmer and is less dense (because it is much cleaner). These differences cause the rivers to meet and not mix. Much later, about 6 kilometres later, these differences attain equilibrium and the rivers merge into the main Amazon river.
Perfect circles of ice have been seen spinning on top of water bodies for quite some time. They aren’t perfectly round most times. Recently, in the month of November last year, a huge 17 meter spinning ice disk was spotted on the river Sheyenne in North Dakota.
Several such ice disks have also been seen in the past in Canada, England and Sweden. Similar ice swirls were also seen in the Charles river, Boston. Some times they are huge, other times you see a number of tiny clusters of such ice swirls.
As always, even ice circles aren’t the work of aliens or government spies. It is completely a natural phenomena which occurs when slowly moving water moves past an obstacle creating a slow moving eddy. In due time, and due to very low temperatures, ice circles form small and keep growing as rings of frozen water on the surface of the water body keeps adding to their diameters. Here’s a video of one such big, and almost perfect, ice circle which was spotted in Rattray Marsh, Canada.
Abraham de Moivre was a famous French mathematician who’s known even today for his de Moivre’s formula. Besides that he’s also known for his work in normal distribution and probability theory.
Moivre’s another area of interest involved making mortality tables. He spent a considerable amount of time connecting death with numbers and was said to have formulated a theory that could predict the day on which a person would die.
When he was 87 years old he noticed a slight change in his sleeping duration. He found that he had started sleeping for 15 minutes more than his usual duration. Each night he was sleeping 15 minutes longer. Putting the math together, he calculated that his sleeping time would add up to 24 hours on November 27th 1754. According to him, when that would happen he would never wake up again. And that is what happened.
De moivre died on November 27, 1754!
Actually, since he had predicted this, out of stubbornness and an obdurate desire to keep up his name as a great statistician, he voluntarily tried everyday to keep up with this 15 minute increase in the sleeping duration everyday. And the day when his total sleep duration added up to 24 hours, he did die. But the official cause of his death was Somnolence (or “sleepiness”).
If luck (or bad luck, if you may call it that) hadn’t favoured him, he would have slept for 24 hours and 15 minutes the other day. In reality, it was his stubbornness and probably sheer luck which put him to an eternal sleep, not math.