HIDE THE CHEESE. A bison-size rodent, Phoberomys pattersoni, grazed on aquatic grasses and roamed the riverbanks of ancient Venezuela about eight million years ago.

THINK the rodents you’ve seen in movies are scary? Scientists who’ve analysed the fossilised remains of an extinct South American relative of guinea pigs say that the ancient bruisers were as large as bison.

Researchers first described Phoberomys pattersoni in 1980 but until recently had only bone fragments and isolated teeth to study. Despite that limitation, scientists suspected that the animals were huge, says Marcelo R. S`E1nchez-Villagra, a paleontologist at the University of T`FCbingen in Germany.

Now, analyses of newly recovered fossils, including a nearly complete skeleton, have enabled S`E1nchez-Villagra and his colleagues to refine estimates of Phoberomys’ size. They put it at about 740 kg, easily earning the species the title of heavyweight rodent of all time. A disproportion between the front and rear limbs suggests that the creature could rest on its haunches and manipulate food with its front paws like its modern relatives do, says S`E1nchez-Villagra.

The new fossils, which the researchers describe in the Sept. 19 Science, were excavated from eight-million-year-old rocks in northwestern Venezuela. The team also unearthed the remains of crocodiles, fish, and freshwater turtles from the same layer of brown shale, says S`E1nchez-Villagra. These companion fossils hint that Phoberomys led a semiaquatic life and probably grazed on aquatic grasses. Examinations of the sediments suggest that the region was probably a river delta surrounded by brackish wetlands, S`E1nchez-Villagra notes.

The contents of ancient pottery could help archaeologists resolve some longstanding disputes in the world of antiquities, thanks to scientists at Britain’s University of Bristol. The researchers have developed the first direct method for dating pottery by examining animal fats preserved inside the ceramic walls.

Archaeologists have long dated sites by the visual appearance of pottery fragments found around the site. The new analytical technique will allow archaeologists to more accurately determine the age of pottery and, by extension, the age of associated artifacts and sites. The research builds on recent work that has shed light on the types and uses of commodities contained within the vessels.

The findings appear in the Sept. 30 edition of Analytical Chemistry, a peer-reviewed journal of the American Chemical Society, the world’s largest scientific society.

Video clips in your newspaper

Imagine opening the newspaper and seeing a full-colour, video clip of a battle or sports match. That’s the sort of vision that drives developers of electronic paper. Even though a black-and-white version that can display static images remains in development, two new approaches offer the prospects of video and bright colour.

Electronic paper is a display technology akin to conventional paper but in which the words and images can be changed at will. Until now, most developers have rolled out prototypes that rewrite images too slowly for video.

Among many e-paper schemes is that of E-Ink of Cambridge, Mass. The company encloses white and black particles inside an array of liquid-filled microspheres. Electrically controlled spheres collectively serve as a pixel in an image. A voltage across a microsphere induces the particles to migrate in opposite directions so that one face of the sphere becomes black and the other white. Reversing the voltage flips the pixel to the opposite configuration.

In the Sept. 25 Nature, Robert A. Hayes and B. Johan Feenstra of Philips Research in Eindhoven, the Netherlands, describe a new type of e-paper pixel. It looks dark when covered by a thin film of colored oil. But when a voltage sweeps the oil into a corner, a bright white surface appears. Pixels one-quarter millimeter on a side can switch between dark and light in less than 15 milliseconds-fast enough for standard video signals.

Come the rainy season and we have millions of fresh young people captivated by the beautiful spectacle of a rainbow. The happening of a rainbow is a phenomenon that lifts the human spirit. It also creates an urge to understand the reasons behind this spectacle. Some people think that understanding such things takes away the romance of the experience. I disagree. For me understanding increases the romance manifold, while imparting it a joyous spring. Let me try to give an answer to your question in a way that does not require a deep knowledge of the science of optics.

We all know that following is true:

* A rainbow is seen only after it has been raining. This suggests that tiny water droplets still hanging in the air might have something to do with the formation of a rainbow. It is easy to see that these droplets cannot be lined up in any fixed direction.

* A rainbow is seen when we stand with the back of our head towards the sun — it is in a direction opposite to the sun. In fact, the only line that we can define in this phenomenon is that which joins our head with the sun.

* The only way the spherical droplets of water can send us some coloured light is if the white light of the sun falling on them is broken up into colours as by a prism and is reflected back in our direction.

* The only preference open to these droplets is to favour some angle with respect to the direction of the incoming rays of the sun; that is the same as the line joining the back of our head and the sun.

* Therefore, democracy and lack of favouritism would demand that the droplets that send us more light are those that lie in an arc around the "our head-sun" direction, That has to be circular in shape — we just intercept half of that in normal rainbows. Any other shape, including a line, is not feasible.

In short, rainbows exist because of a preference in favour of a specific angle that depends on the properties of water and shape of droplets. This is the so-called "angle of minimum deviation" while passing through a prism. For water droplets this happens to be about 42 degrees.

When the nib of a fountain pen touches a drop of ink, the ink moves up into the nib. Why?

The nib and its holder provide an interconnected labyrinth of capillaries near the writing end of a fountain pen. The ink is sucked in because of a capillary force, much like the way oil moves up in the wick of a kerosene lamp or sap through the tiny pathways in the stems and trunks of plants and trees. In fact a fountain pen writes on paper because the tinier capillaries on the surface of the paper suck in the ink from the pen. You must have noticed that it is difficult to write on a smooth glass plate using a fountain pen! I might mention that the basic reason for capillarity is the surface tension of water — which in turn is produced by the unbalanced intermolecular attraction at the surface of a liquid.