The case of the drowning crickets

A firebelly toad waiting for a cricket

Our aquatic tank contains many firebelly toads, and each one of them is a voracious cricket eater. A few large rocks in the tank create an island, surrounded by open water. When we place crickets on the rocks, a significant portion of them fall into the water staying there until they drown (or until we rescue them and put them back on solid ground). Are cricket brains so tiny that they don’t realize they can’t breathe, and so don’t pull themselves out of the water, or is something else going on?

I found a nice explanation in an essay by J.B.S. Haldane (1892-1964) ‘On Being the Right Size’:

There is a force which is as formidable to an insect as gravitation to a mammal. This is surface tension. A man coming out of the bath carries with him a film of water of about one-fiftieth of an inch in thickness. This weighs roughly a pound. A wet mouse has to carry about its own weight in water. A wet fly has to lift many times its own weight and, as everyone knows, a fly once wetted by water or any other liquid is in a very serious position indeed. An insect going for a drink is in as great danger as a man leaning out over a precipice in search of food. If it once falls into the grip of the surface tension of the water - that is to say, gets wet - it is likely to remain so until it drowns.

I often swim at lunch. When I’m done I haul myself out of the water and head to the showers without a second thought for the amount of pool water I’m carrying around with me. It’s lucky for me that my size makes me immune to the same surface tension that drowns the unfortunate crickets.

As a tangent: I found an online copy of Haldane's essay here - it's worth reading and not too long.

Swamp Water

Home for many microbes

On a whim, I did an internet search on 'swamp water'. What came up included alcoholic drink concoctions and a 1941 movie based on an earlier book which looked like more of a drama than the potential horror promised in the title. No search result came up for swamp water as the random mixing of soda pops (which always came out brown for me because of the necessity of root beer). When I was a kid, I looked forward to any opportunity to mix pops and called it 'swamp water'. I did an informal survey of friends, and I'm not the only one who made swamp water, in fact, a few friends admitted they still do it, especially with slurpees. It even turns out some kids today are still making swamp water.

Speaking of kids and swamp water, I ran a group activity for kids last week on microbes (specifically the oceanic variety, although discussions didn't go that way). I borrowed a microscope and brought in water wrung out of my aquarium's filter, otherwise known as my in-house swamp water. The whole activity reminded me of when I was kid and my science-teacher father brought home a microscope from work for me to use. All the little critters out of my aquarium's filter became visible to me.

We haven't always known about microbes. Anton van Leeuwenhoek (I have no idea how to pronounce his name) discovered these tiny life forms everywhere in 1675. For his discovery, he used a microscope of his own design – one of the earliest microscopes. By definition microbes are simply creatures you need a microscope to see, and they typically form the base of an ecosystem. According to Wikipedia, many blame the failure of Biosphere II on an improper balance of microbes. Microbes are incredibly useful: they are required for brewing, wine making, baking, pickling and fermentation; they play a role in decomposition of organic matter; and they aid our own digestion by synthesizing vitamins and fermenting complex carbohydrates into digestible form. Microbes aren't all beneficial, in fact, many infectious diseases can be attributed to them.

My favourite of the aquarium-filter microbes are amoeba, partly because I can identify them and partly because they lack a definable shape. They are moving blobs that use their blobiness to envelope their prey. Amoeba were discovered by August von Rosenhof (another name I can't pronounce) in 1757, a surprisingly long time after the discovery of microbes especially considering how ubiquitous they are (in every aquarium I've ever had amoebas have flourished).

With the exception of amoeba, I can't identify specific microbes. They are hugely diverse: there are ones that swim like snakes, ones shaped like tiny ovals zooming around, and ones formed as large blobs that change shape as they move – plus many more. And this is just in my aquarium (which was originally seeded from local pond water). What would I find in my soil? Under the oak leaves in the park nearby? In a tidal pool? How about in my kitchen sink's drain? I'm always amazed by the diversity of critters right under our noses (or even in our noses). We live in a wild place.

Buckets of water

I was asked why a bucket full of water looks shallower than an empty one, so I pulled out an old physics book to find the answer. It's been many years since I've taken optics, although recently I've developed a new interest for it.

Refraction occurs because the speed of light changes based on the density – something I discussed here. The refractive index is the ratio of the speed of light in a vacuum to the speed in the medium. If we think about water with its refractive index of 1.33, we find that light travels 1.33 times faster in a vacuum than the water. The denser the medium, the greater the difference in speed of light and the bigger the refractive index.

Not only does light slow down, it also bends. When a ray of light hits a surface at an angle (angle of incidence) it gets bent to a new angle (angle of refraction) inside the surface. With a little trigonometry applied to these angles, we find that their ratio is also the refractive index, a trick discovered by Willebrod Snellius (of Snell's law fame) in 1621 – although an Arab scientist figured this out almost 500 years earlier.

So, what fun can we have with the refractive index? Ever looked into a still pool of water? Due to light rays bending in the water, the pool will look ¾ the depth it actually is. If a post sticks up through the water, it will look oddly disjointed at the surface – appearing to extend at one angle above the water and another below the surface even through the pole is straight.

From another point of view, what does a fish see when it looks up? A fish sees a lot more than expected. By looking up in a cone of 98 degrees, a fish gets a 180 degree view above the water due to refraction. The view above the water would be strange – someone fishing on the shore would look excessively squat, standing at an odd angle and probably distorted due to ripples on the surface. But, the fish would see the fisherman, making it much more difficult to be successful at fishing (spear fishing is even more complex due to refraction). By the way, if you put on your goggles and hopped into the local swimming pool, you would see what the fish sees.

What makes water wet?

Water is pretty fabulous stuff. It makes life possible and over enough time acts as a universal solvent. On earth, water is everywhere from the glass on my desk to covering over 70% of the surface. Oceans contain approximately 1,360,000 cubic kilometers worth of water – a lot of water even before land based, sub-surface, frozen or any other place water hides is considered.

Our current understanding of water came relatively recently. We held onto the ancient Greek concept that water was one of the four basic elements (along with fire, earth and air) up until the Renaissance. Water is very stable, making it difficult to break into its parts, but it was done at a time when most people considered it a fundamental element. The French chemist Lavoisier managed to break water apart into its components (two hydrogen molecules and one oxygen on) on 28 February 1785. In time it was determined that covalent bonds hold water together, that is, by sharing electrons between atoms.

A water molecule resembles Mickey Mouse's head. Two ears on top, which are hydrogen atoms, and the head would be the oxygen atom. The top, where the hydrogen is, is somewhat positive and the bottom, where the oxygen is, is somewhat negative resulting in a polar molecule. Since positive and negative are attracted to each other a hydrogen atom from one water molecule is attracted to the oxygen atom of a neighboring water molecule.

How many water molecules must we have before it can be called a liquid? In the field of fluid mechanics, they have what is called a 'continuum hypothesis'. This hypothesis assumes that to be a fluid there must be over a million water molecules present within a reasonable volume (by reasonable, I mean some where between packing them in so tightly they become like a black hole or spreading them out so much it looks like a vacuum).

So, assuming we have enough water molecules to make a liquid, let's think about putting them all into a glass of water. In the middle of the glass, each water molecule attracts its neighboring molecules (remember the polar trait from above). This attraction occurs from all direction at once, resulting in a balance and no net force. Things don't work out so nicely at the surface. Here, the attraction doesn't balance because there is only attraction from the molecules to the sides and below as there are no water molecules above the surface. This causes surface tension. Molecules at the surface are pulled towards the center of the liquid, minimizing the surface area. A very small drop of water pulls itself into a sphere because a sphere has the smallest ratio of surface area to volume. Water in a glass will form a flat surface (ignoring the meniscus) as it is the minimum space it can take up.

Since wet is defined as 'consisting of, containing, covered with, or soaked with liquid (as water)'. Water acts to makes something else wet (as opposed to being wet itself) – so if I go walking outside on a rainy day, I end up wet from the rain.

Can we come up with a better way?

I've been thinking a lot lately about ways I can reduce my ecological footprint and I have some ideas.

I've been reading 'Water, A Turbulent History' by Stephen Halliday, a book I randomly found in the library. I was looking for books on how to improve my house's energy efficiency in the engineering section and I found a history book. I was intrigued by the title so I signed it out. How he describes water pollution by sewage got me thinking.

In 1357, King Edward III decreed 'no man shall take any manner of rubbish, earth, gravel or dung out of his stables or elsewhere to throw and put the same into rivers Thames or Fleet'. Due to this attitude, up until the early 1800's, the Thames and its tributaries remained reasonably clear of pollution.

In London during these times, human waste was removed by dedicated workers called 'nightsoilmen'. These men carted away the waste at night and sold it to farmers as manure. Apparently, they earned a decent pay for their work. Then things changed for the nightsoilmen. Competition was introduced when bird guano was imported from South America, starting about 1840. The guano was easier to work with for the farmers and had less of a smell. About this time, having a water closet in your home became a status symbol.

Water closets were invented in the 16th century by Sir John Harington, who made two. One of which was given to Queen Elizabeth I. She didn't like it because the loudness of the flushing announced to everyone when she used it. Without a royal stamp of approval, the water closet became a neglected idea until early in the nineteenth century.

When a water closet is flushed there is only a little 'waste' for 10-20 times the volume of water. The nightsoilmen found this wet waste hard to collect and transport and the farmers no longer wanted it. Cesspools now overflowed into the waterway, polluting them. Cholera epidemics followed and ultimately sewer systems were built.

So now what was once composted (and likely still is in many parts of the world) is now diluted with water and washed away through dedicated pipes buried beneath the ground by gas guzzling equipment. Sewage ultimately ends up at a dedicated treatment plant of some sort that no one wants to be a neighbour to. At any point a leak could pollute our water ways and in many places this has happened. There must be a solution for urban dwellers that doesn't require fancy infrastructure or lots of a critical resource such as water. I realize human waste can carry disease, but is watering it down and flushing it away the best way to deal with it?

It's snowing

It's snowing like mad out and very windy. In my backyard, the periodic wind gusts whip up the snowflakes into whirls and eddies producing momentary white outs. Fortunately, I don't have to go anywhere today. It doesn't snow often where I live, usually it remains green throughout the year. When it does snow it's like magic to me, the landscape is transformed from green to white like a idyllic Christmas card. The world seems hushed and new.

Today, the snow flakes are medium in size – not like our usual massive wet flakes that vanish once they hit the ground, or like the tiny prairie snowflakes that can be swept away with a broom. Each snowflake is a wonder of sharp-edged geometry. I don't know if each snowflake is truly unique or not – but I accept that it could be true. What I do know is that snow is just water and knowing this doesn't take away from the magic of a snow storm (if I'm inside).

Snow is just water – school children know this (hopefully, they also know about the perils of yellow snow). Winter outdoor survival manuals warn against eating snow directly only because it is cold – they just want you to melt it first.

I found a paper from 1673 on 'some observations touching the nature of snow' by N. Grew in the Philosophical Transactions of the Royal Society of London. He questions how snowflakes form and their geometry. He deduces that snowflakes come from icicles that form inside snow clouds. As they descend they thaw a bit, bump together and break apart eventually becoming the snowflakes we know.

For our modern view of how snowflakes form check out this.

Water drops on kale

I was out in my garden this morning in the few moments of sun before more rain and I noticed beads of rain water had formed on the kale leaves. See how the veins on the leaf are moved when looked at through the water? See the sky reflection? If I had leaned close enough, my reflection would probably be visible too.

My glass of water

A glass of water sits on my desk. The glass is clear and the water is clear, therefore the boundaries between them vanish. Instead of pondering if my glass is half-full or half-empty, I'm thinking about the water. In my glass, sitting still on my desk, the water looks like such a simple thing, but it is composed of zillions of tiny molecules of two atoms of hydrogen and one of oxygen pinned together like Micky-Mouse ears.

A single molecule of water is quite dull to the non-chemist like myself. But, put together a bucketfull of these molecules and an exciting thing happens: liquidity. The molecules slosh as one, they fill the nooks and cranies of their container completely and can disolve almost anything given enough time. Along with gases, liquids are considered a fluid. Their physical properties (like density and pressure) are continuous, there are no gaps or instantaneous changes occuring thoughout their volume. Like projectiles and pendulums, fluids follow Newton's laws. Mass, energy and momentum are all still conserved but, the equations describing their motion are exceptionally complex for even the simplest case.

If I drop a stone in the center of my glass a circular ripple will move outwards, taking the information about the pebble's disturbance to the edge of the glass, where it will be reflected back. This ripple is a type of wave, and though it looks like the water is moving outwards, it isn't. Instead, each water particle moves up and down, then its neighbor moves up and down next – exactly like what happens in a stadium when the audience does the wave. If I blew on the surface of the water, I would create similar waves, except this time they would be moving in one direction instead of radially away from a point. In the ocean, you get waves created this way by the wind. The waves formed can move across entire ocean basins and crash against distant shores long after the wind that formed them has stopped blowing.

If, instead of a stone, I released a drop of dye into my completely still glass of water, a different effect would occur. The momentum of the dye dropping would take the dye down into the middle of the glass. From there it would spread out in random tendrils, the edges between the dye and the water would become blurred and ultimately I would have a homogeneous (evenly mixed) solution of dye and water. But I haven't stirred or disturbed the water in the glass, so how does the dye get evenly mixed in? It is because I keep my office well above absolute zero, so the water and dye particles in the glass all have thermal energy, and this energy causes the particles to move. At the dye-water boundary, some of the dye will move out into the water and some of the water will move into the dye, blurring this boundary. With enough time this effect, diffusion, will completely mix the dye and water.

To mix in the dye faster I could stir the water in a constant circle with a chopstick. When I pull out the chopstick, the water would continue moving in a circle, which is also called an eddy, whirlpool, or vortex. The edges would be higher than the center because of centrifugal forces, that is, each water particle, once set into motion, wants to move in a straight line until it encounters the glass edge. At the edge, there is no choice except to move in a circle. A similar effect would occur if you spun the glass, or in the case of the oceans, spun the globe beneath. The effect of the spinning earth is called the coriolis force (which isn't really a force) and creates eddies in the ocean basins that spin in different directions in the north and south hemisphere. When you flush your toilet, a whirlpool often forms, but its direction doesn't depend on the hemisphere, instead it is dependent on the conditions within the toilet itself.

Perhaps I want to mix my dye and water even faster, so I put a lid on the glass and shake it. The moving water would stretch the boundary with the dye in random directions, creating more boundary surface area allowing for faster diffusion. The sloshing water can be described as turbulent, that is, the flow interacts with itself creating an element of randomness and becomes chaotic.

What I find most interesting about water, especially in the ocean, is that all of these phenomenon can happen at the same time and at all scales. On a tiny scale there can be turbulence, on a slightly larger scale there can be eddies, larger scales still may contain waves. Ultimately we reach the scale of tides, but that is a topic for another day.