TPO 17 Lecture 3
History(Ancient Egyptian Calendar)
Narrator
Listen to part of a lecture in a history class. The professor has been discussing ancient Egypt.
Professor
Ok, so one of the challenges that faced ancient civilizations like Egypt was timekeeping, calendars. When you have to grow food for whole cities of people, it is important to plant your crops at the right time. And when you start having financial obligations, rents, taxes, you have to keep track of how often you pay.
So today we will look at how the Egyptians adressed these problems. In fact, they ended up using two calendars, one to keep track of the natural world, or their agriculture concerns, and another one, that was used to keep track of the business functions of the Kingdom. So let’s take a look at the hows and whys of one ancient Egyptian calendar system, starting with the Nile River.
Why the Nile? Well, there’s no other way to put it. Egyptian life basically revolved around the mysterious rise and fall of the river. The success of their agriculture system depended upon them knowing when the river would change. So, naturally，their first calendar was divided up into three seasons, each based on the river ’s changes: inundation, subsidence and harvest.
The first season was the flooding, or inundation, when the Nile valley was essentially submerged in water for a few months or so. And afterwards during the season of subsidence, the water would subside, or recede, revealing a new layer of fertile black silt and allowing for the planting of various crops. And finally the time of the year would arrive when the valley would produce crops, such as wheat, barley, fruit, all ready to harvest. Ok, so it was important to the ancient Egyptians to know when their Nile based seasons would occur, their way of life depended upon it.
Now, the way they used to count time was based on the phases of the moon, which，regularly and predictably, goes through a cycle, starting with a new moon, then to a full moon, and back again to the new moon. Now this cycle wes then used to determine the length of their month. So, um, one lunar cycle was one Egyptian month, and about four of the months would constitute a season. Now, 12 of these months was an approximately 354-day year. So they had a 354-day agricultural calendar that was designed to help them determine when the Nile would inunadate the land.
Well, of course it had to be more complicated than that. The average amount of time between floodings wasn’t actually 354 days. I mean, although it varies, the average was clearly longer than 354 days. So how did they keep this short calendar in step with the actual flooding of the Nile?
Well, their astronomers had discovered that at a certain time of year the brightest star, Sirius, would disappear. Actually, it’d be hidden in the glare of the Sun. And then，a couple of months later, one morning in the eartern sky just before dawn, Sirius would reappear. And it happened regularly, about every 365 days. Even more significantly, the reappearance of Sirius would occur around the same time as the Nile’s flooding. And this annual event is called a heliacal rising.
The heliacal rising was a fair indicator of when the Nile would flood. The next new moon, after the heliacal rising of Sirius, which happened in the last month of the calendar year, marked the New Year. And because the ancient Egyptians were using the lunar cycle in combination with this heliacal rising, some years ended up having 12 lunar months, while others had 13 lunar calender months, if Sirius didn’t rise in the 12th month.
Even though the length of the agricultural calendar still fluctuated, with some years having 12 months and others having 13, it ended up being much more reliable than it was before. They continually adjusted it to the heliacal rising of Sirius, ensuring that they never got too far off in their seasons. This new calendar was ideal, because, well，it worked well for agricultural purposes as well as for knowing when to have traditional religious festivals. So, that was their first calendar.
But was it any way to run a government? They didn’t think so. For administrative purposes, it was very inconvenient to have years of different lengths. So another calendar was introduced, an administrative one. Probably soon after 3,000 BC, they declared a 365-day year, with 12 months per year, with exactly 30 days each month, with an extra 5 days at the end of each year. This administrative calendar existed alongside the earlier agricultural and religious calendar that depended on the heliacal rising of Sirius. This administrative calendar was much easier to use for things like scheduling taxes and other things that had to be paid on time. Over time，the calendar got out of step with seasons and the flooding of the Nile, but for bureaucratic purposes, they didn’t mind.
TPO 17 Lecture 4
Biology(Octopus)
Narrator
Listen to part of a lecture in a biology class.
Professor
Ok, now I want to talk about an animal that has a fascinating set of defense mechanisms. And that's the octopus, one of the unusual creatures that live in the sea.
The octopus is prey to many species, including humans, so how does it escape its predators?
Well, let me back up here a second. Anyone ever heard of Proteous? Proteus was a God in Greek mythology who could change form. He could make himself look like a lion or a stone or a tree, anything you wanted, and he could go through a whole series of changes very quickly.
Well, the octopus is the real world version of Proteus. Just like Proteus, the octopus can go through all kinds of incredible transformations. And it does this in three ways: by changing color, by changing its texture, and by changing its size and shape.
For me, the most fascinating transformation is when it changes its color. It's a normal skin color, the one it generally presents, is either red or brown or even grey, and it's speckled with dark spots. But when it wants to blend in with its environment to hide from its enemies, it can take on the color of its immediate surroundings: the ocean floor, a rock, a piece of coral, whatever. Charles?
Student
Do we know how that works, I mean, how they change colors?
Professor
Well, we know that the reaction that takes place is not chemical in nature. The color changes are executed by two different kinds of cells in the octopus' skin, mainly by color cells on the skin's surface call chromatophores
Chromatophores consist of tiny sacks filled with color dye. There might be a couple hundred of these color sacks per square millimeter of the octopus' skin, and depending on the species, they can come in as many as five different colors. Each one of these sacks is controlled by muscles. If the muscles are relaxed, the sack shrinks, and all you see is a little white point. But if the muscle's contract, then the sack expands, and you can see the colors. And by expanding different combinations
Student
And just with various combinations of those five colors, they can recreate any color in their environment?
Professor
Well, they can no doubt create a lot with just those five colors, but you are right, maybe they can't mimic every color around them, so that's where the second kind of cell comes in.
Just below the chromatophores is a layer of cells that reflect light from the environment, and these cells help the octopus create a precise match with the colors that surround them. The colors from the color sacks are supplemented with colors that are reflected from the environment, and that's how they are able to mimic colors with such precision. So, that's how octopus mimic colors.
But they don't just mimic the colors in their environment; they can alos mimic the texture of objects in their environment. They have these little projections on their skin that allow them to resemble various textures. The projections are called papillae. If the octopus wants to have a rough texture, it raises the papillae. If it wants to have a smooth texture, it flattens out the papillae, so it can acquire a smooth texture to blend in with the sandy bottom of the sea.
So the octopus has the ability to mimic both the color and the texture of its environment. And it's truly amazing how well it can blend in with its surroundings.
You can easily swim within a few feet of an octopus and never see it.
Student
I read that they often hide from predators by squirting out a cloud of ink, or something like that.
Professor
Yes. The octopus can release a cloud of ink if it feels threatened. But it doesn't hide behind it, as is generally believed. Um, the ink cloud is ... it serves to distract a predator while the octopus makes its escape.
Um, now there's a third way that octopus can transform themselves to blend in withor mimic their environment, and that's by changing their shape and size, well, at least their apparent size.
The muscular system of the octopus enables it to be very flexible to assume all sorts of shapes and postures. So it can contract into the shape of a little round stone, and sit perfectly still on the seafloor. Or it can nestle up in the middle of a plant and take the shape of one of the leaves. Even Proteus would be impressed, I think.
