Comparisons – Page 33 – Science-Education-Research

observing a cell nucleus is like revealing invisible writing

An example of an analogy used in a popular science book:

"Each cell contains in the its interior a small spherical body known as the nucleus, which is formed by a fine network of the substance known as chromatin. It must be noticed here that various parts of the protoplasm forming the body of the cell have under normal circumstances equal optical transparencies so that the structure cannot be observed simply by looking at a living cell through a microscope. In order to see the structure we have to dye the material of the cell, taking advantage of the fact that different structural parts of the protoplasm absorb the dyeing materials in various degrees. The material forming the network of the nucleus is especially susceptible to the dyeing process, and appears clearly visible against the lighter background.

You can see a similar method by writing something on a piece of paper with a wax candle. The writing will be invisible until you try to shade the paper with a black pencil. since the graphite will not stick to the places covered with wax the writing will stand out clearly on the shaded background."

George Gamow (1961) One, Two, Three…Infinity. Facts and speculations of science, Revised Edition, Dover Publications, Inc., New York.

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salt molecules are kicked out of supersaturated solution

An example of a simile used in popular science writing:

"If, for example, we drop a small salt crystal into a supersaturated salt solution in water, the crystal will grow by adding to its surface successive layers of salt molecules extracted (or rather 'kicked out') from the water.

…

The molecules of salt that were previously mixed with water molecules simply collect themselves on the surface of the growing crystal."

George Gamow (1961) One, Two, Three…Infinity. Facts and speculations of science, Revised Edition, Dover Publications, Inc., New York.

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Many examples of science similes are listed in 'Creative Comparisons: Making Science Familiar through Language. An illustrative catalogue of figurative comparisons and analogies for science concepts'. Free Download.

Salt is an ionic substance, so does not form molecules under usual conditions. The crystal grows by the addition of ions, not molecules. The solution contains hydrated sodium ions and hydrated chloride ions, not molecules. (Elsewhere in the same book Gamow suggests solid salt contains atoms of sodium and chlorine – a different misconception!)

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cells are biological atoms

An example of an analogy employed in popular science writing"

"These elementary structural units of living matter are usually known as 'cells'; they could also be called 'biological atoms' (i.e., 'indivisibles') in the sense that the biological properties of a given type of tissue will be retained only so long as it contains at least one individual cell.

A muscle tissue, for example, which is cut to the size of only half of one cell, would lose all the properties of muscular contractions, and so on, exactly in the same way as a piece of magnesium wire containing only one half of a magnesium atom would no longer be magnesium metal, but rather a small piece of coal."

George Gamow (1961) One, Two, Three…Infinity. Facts and speculations of science, Revised Edition, Dover Publications, Inc., New York.

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This analogy is based upon the explicit idea that a tissue comprising a single cell retains its properties (surely questionable in many cases?), and the implied suggestion that an element sample of a single atom would retain its chemical properties. The latter is a common form of misconception (a 'macro-micro confusion) where it is assumed that bulk properties reflect the properties of the individual atoms or molecules, rather than emerging from large numbers of them interacting.

It is not possible to have a wire of a single atom, and a single atom of magnesium does not have the properties of bulk magnesium And 'half a magnesium atom' may be a carbon atom, but it is not a small piece of carbon (as in graphite, diamond…) and it certainly is not a piece of coal which is not even a form of pure carbon.

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bacterium experiences molecular impacts as if in an excited crowd

An example of an analogy used in popular science writing:

"Certainly a bacterium, which through all its life is tossed around by molecular impacts, will sneer at the statement that heat cannot go over into mechanical motion! … For a bacterium, which is not much larger than the molecules themselves, the difference between the thermal and mechanical motion has practically disappeared, and it would consider the molecular collisions tossing it around in the same way as we would consider the kicks we get from our fellow citizens in an excited crowd."

George Gamow (1961) One, Two, Three…Infinity. Facts and speculations of science, Revised Edition, Dover Publications, Inc., New York.

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This passage could be seen as anthropomorphic, in suggesting that a bacterium (a single celled entity with no nervous system) could sneer or give consideration to water molecules colliding with it.

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The suggestion that a bacterium is not much larger than the molecules colliding with it could be misleading. Some learners will have the alternative conception that cells may not be so much bigger than atoms (read 'The cell nucleus is probably bigger than an atomic nucleus: A cell is about ten times larger than an atom'), but a quick 'back-of-the-envelope' calculation suggests that if a bacterium is of mass c.1.7 x 10^-13g (a value given for E. coli in one research paper) then as the mass of a water molecule is 18g/N_A or c.3 x 10^-23g which would suggest each bacterium is about the mass of 5 000 000 000 water molecules. By most reasonable uses of language a bacterium is much larger than the molecules.

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molecule in liquid is like a little drunkard

An example of a simile used in popular science words:

"To make such motion visible one must use two different kinds of molecules distinguishable for example by their different colours.Thus we can fill one half of a chemical test tube with a water solution of potassium permanganate, which will give to the water a beautiful purple tint. If we now pour on the top of it some clear fresh water, being careful not to mix up the two layers, we shall notice that the colour gradually penetrates the clear water. If you wait sufficiently long you will find that all the water from the bottom to the surface becomes uniformly coloured. This phenomena, familiar to everybody, is known as diffusion and is die to the irregular thermal motion of the molecules of dye among the water molecules. We must imagine each molecule of potassium permanganate as a little drunkard who is driven to and fro by the incessant impacts received from other molecules."

George Gamow (1961) One, Two, Three…Infinity. Facts and speculations of science, Revised Edition, Dover Publications, Inc., New York.

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Gamow refers to 'molecules' of potassium permanganate. Potassium permanganate is a salt, so is composed of ions, and will be dissociated in aqueous solution. The colour is due to the permanagnate ion – hydrated potassium ions also diffuse, but as they do not give rise to any colour this cannot be detected. Gamow, as a research physicist, was likely using 'molecule' generically without distinguishing between actual molecules and ions, but many learners assume all materials, including salts, will be molecular so this is a common alternative conception (misconception).

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solid matter is a magnificent building

An example if extended metaphor in popular science writing:

"Thus we see the effect of thermal agitation is to destroy step by step the elaborate architecture of matter based on the law of quantum, and to turn this magnificent building into a mess of widely moving particles rushing around and colliding with one another without any apparent law of regularity."

George Gamow (1961) One, Two, Three…Infinity. Facts and speculations of science, Revised Edition, Dover Publications, Inc., New York.

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Many examples of science metaphors are listed in 'Creative comparisons: Making science familiar through language. An illustrative catalogue of figurative comparisons and analogies for science concepts'. Free Download.

liquid molecules crawl like worms

An example of simile used in science writing:

"The breaking up [on heating] of the beautiful crystalline structure of solid bodies forces the molecules first to crawl around one another like a pack of worms, and then fly apart as though they were a flock of frightened birds."

George Gamow (1961) One, Two, Three…Infinity. Facts and speculations of science, Revised Edition, Dover Publications, Inc., New York.

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molecules in a solid are like angry dogs on short chains

An example of analogy in popular science writing:

"Although in the solid state of matter the molecules are strongly bound to their places [sic], it does not mean at all that they are not affected by thermal agitation. Indeed, according to the fundamental law of heat motion, the amount of energy in every molecule is the same for all substances, solid, liquid, or gaseous at a given temperature, and the difference lies only in the fact that whereas in some cases this energy suffices to tear off the molecules for their fixed positions and let them travel around, in other cases they can only quiver on the same spot as angry dogs restricted by short chains."

George Gamow (1961) One, Two, Three…Infinity. Facts and speculations of science, Revised Edition, Dover Publications, Inc., New York.

I was unsure whether to consider this a fully-blown analogy or just an extended metaphor. There is a mapping between target and analogue (angry dogs – molecules in solid; quivering – thermal agitation; short chains – strong bonding), but it is not made very explicit for a non-specialist reader.

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water molecules are like people in an excited crowd

An example of simile (and anthropomorphic metaphor) in popular science writing:

"…it is also apparent that the water is far from still, and that its molecules are in a state of violent agitation moving around and pushing one another as though they were people in a highly excited crowd. … For those organisms that are much smaller than human beings, such as, for example, small bacteria suspended in a water drop, the effect of thermal motion is much more pronounced, and these poor creatures are incessant kicked, pushed, and tossed around by the restless molecules that attack them from all sides and give them no rest…"

George Gamow (1961) One, Two, Three…Infinity. Facts and speculations of science, Revised Edition, Dover Publications, Inc., New York.

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The description here is anthropomorphic in that language is used which is more appropriate for sentient people than water molecules or bacteria (e.g. that molecules kick or attack bacteria is only metaphor; the notion of rest makes sense to us, but is questionable when applied to a bacterium.)

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U-238 acts like water in wet wood

An example of an analogy and metaphor employed in popular science writing:

"…U-235 does not exist in nature in a pure form, and is always found to be strongly diluted by the heavier unfissionable isotope of uranium, U-238 (0.7 per cent of U-235 and 99.3 percent of U-238), which hinders the development of the progressive chain reaction in natural uranium in the very same way as the presence of water prevents wet wood from burning. …

"…if we could do something to prevent the nuclei of U-238 from kidnapping the neutrons before they have a chance to meet a U-235 nuclei, which could cause their fission, the problem would be solved."

George Gamow (1961) One, Two, Three…Infinity. Facts and speculations of science, Revised Edition, Dover Publications, Inc., New York.

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neutrons could multiply like rabbits or bacteria

An example of an analogy employed in popular science writing:

"If it were possible to have neutrons kick out neutrons and to do it in such a way that each neutron would produce more than one offspring, these particles would multiply like rabbits…or bacteria in infected tissue, and the descendants of one single neutron would soon become sufficiently numerous to attack every single atomic nucleus in a large lump of material. …

"In order to satisfy the condition for progressive breeding it is apparently necessary that out of, say, a hundred neutrons entering into the substance we should get more than a hundred neutrons of the next generation."

George Gamow (1961) One, Two, Three…Infinity. Facts and speculations of science, Revised Edition, Dover Publications, Inc., New York.

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The references to neutrons having offspring and descendants are metaphorical, but align with the analogy to reproduction.