Comparisons – Page 27 – Science-Education-Research

governor balls are attached by rods like a pair of tongs

An example of a simile used to explain a scientific idea:

"…the governor. This consists of an upright spindle, which is kept constantly turning, by being connected with a certain part of the machinery, and from which two balls are suspended in opposite directions by rods, attached by joints, somewhat in the manner of the legs of a pair of tongs. As long as the motion of the engine is uniform, that of the spindle is so likewise, and the balls continue steadily revolving at the same distance from each other. But as soon as any alteration in the action of the piston takes place, the balls, if it has become more rapid, fly further apart under the influence of the increased centrifugal force which actuates them – or approach nearer to each other in the opposite circumstances."

George L. Craik (1830) James Watt, reprinted in Cochrane, R. (Ed.). (1897). Heroes of Invention and Discovery. Lives of eminent inventors and pioneers in science. W. P. Nimmo, Hay, & Mitchell.

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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.

The passage also contains an alternative conception as the force which causes the balls to rotate is centripetal (causing an acceleration towards the centre) not centrifugal. Confusing the governor is also widely known as both the centripetal governor and (inappropriately as) the centrifugal governor.

Read about conceptions of centripetal force

image of engine governor showing the two weights (balls) — Ashton Frost engine governor [source: https://en.wikipedia.org/wiki/Governor_(device)]

coral reefs probably grow like forests

An example of analogical thinking in science:

"Any facts which can elucidate the rate at which corals can grow under favourable circumstances, will ever be interesting: nor should negative facts, showing that within a given period reefs have not increased either laterally or vertically upwards, be neglected. In a full-grown forest, to judge of its rate of growth, a part must be first cut down; so is it probably with reefs of corals. The aborigines of some of the many coral islands in the great oceans might perhaps adduce positive facts on this head; for instance, the date might be known when a channel had been cut to float out a large canoe, and which had since grown up."

Charles Darwin (1849) Section VI: Geology. In Herschel, J. F. W. ed., A manual of scientific enquiry; prepared for the use of Her Majesty's Navy: and adapted for travellers in general. London: John Murray.

Here Darwin is not using analogy to explain a scientific idea, but rather to form a scientific hypothesis.

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

expanse of salt as white as newly fallen snow

An example of simile used in science writing:

"The salt from the Rio Negro, from the S. Chiquitas and from San Julian, instead of being an "amorphous mass," yielding "a soft powder," is coarsely crystallized, some of the cubes being even 3 or 4 inches square. Instead of being mixed with much earth, the salt presents an expanse as white as newly fallen snow, which, viewed from a distance, as I well remember to my cost, might readily be mistaken for a lake."

Charles Darwin (1847) Salt. Gardeners' Chronicle and Agricultural Gazette.

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worm-holes nearly as large as swan-quills

Examples of quotidian comparisons in science writing:

"When digging in this field, after a long drought, I noticed, that one single clod of earth, about as large as a man's two hands, was penetrated by eight upright, cylindrical worm-holes, nearly as large as swan-quills, so that I could see through them."

Charles Darwin (1844) On the origin of mould. Gardeners' Chronicle and Agricultural Gazette

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comb of bristle-like teeth found on each arm of the horse-shoe

An example of the use of simile in scientific descriptions of the natural world (here a group of arrow worms):

"The head when not in action is slightly flattened and of a truncate-conical shape; when in action its basal part assumes a semilunar or horse-shoe form, in the concavity of which lies the longitudinally-folded mouth. On each arm of the fleshy horse-shoe, a comb, formed of eight strong, curved, slightly hooked claws or teeth, is attached. The animal when lively is constantly clasping these bristle-like teeth together, over its mouth; when clasped together, and the head in a state of inaction, they appear to be situated much nearer to the mouth than when their fleshy bases are expanded in action.
…
The animal moves quickly by starts, bending its body. The two pair of lateral fins and that on the tail lie in the same horizontal plane: viewed with a lens of small power they appear formed of a delicate membrane, but under a lens of 1/20th of an inch focal distance they appear to consist of excessively fine transparent rays, touching each other, like the barbs of a feather, but not, as it appeared to me, actually united by a membrane.
…
When the tail is filled with vigorously circulating matter two large cul-de-sacs or gut-shaped ovaries are invariably present, extending, as represented (o o) in the diagram, from the base of the tail along each side of the intestinal tube…"

Charles Darwin (1844) Observations on the structure and propagation of the genus Sagitta. Annals and Magazine of Natural History

Biological descriptions often include comparisons to more familiar structures (e.g., 'like the barbs of a feather'). The reference to "the fleshy horse-shoe" would seem to be a metaphor (that is, the structure is here described as, not like, a horseshoe), except that Darwin had already made the comparison to a half-moon or horse-shoe explicit.

I have included the reference to the cul-de-sac which may seem to be another metaphor – but the term culd-de-sac was used in anatomy as a technical term and alternative to diverticulum to label a sac or pouch connected to a hollow organ. To refer to the head part as having an arm could be considered metaphorical, though this is a common usage and so would be likely read as literal.

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image of Sagitta — Sagitta (By Zatelmar – Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=2777766)

divided stigma of flower licks the back of the entering bees

An example of figures of speech used in writing about science:

"Let any one who doubts the use of bees in the fructification of hermaphrodite flowers, watch and admire the manner in which the flat surface of the divided stigma of this Mimulus licks the back of the entering bees, which is generally well-dusted already with pollen; and then how admirably the two divisions of the stigma, endowed with a sensitive faculty, close like a forceps on the included granules of pollen!"

Charles Darwin (1841) Humble-bees. Gardeners' Chronicle and Agricultural Gazette

Licking strictly refers to the tongue, so here lick is used as a metaphor.

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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.

The reference to the stigma closing like a forceps is a simile.

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vaporising an earth-bound asteroid is a Hail Mary approach

An example of figures of speech used in public science discourse:

"…if you punch an earth-bound asteroid too hard, it will fragment into several smaller but still dangerously sized pieces, effectively turning a cannonball into a shotgun spray. For bigger asteroids or for smaller earth-bound asteroids discovered with little warning time something with more oomph may be required: a nuclear weapon. Park a nuke-armed spacecraft next to the asteroid, detonate, and one side of it [the asteroid] will become severely irradiated. That side will shatter and jettison debris into space, pushing the asteroid away from earth as if it were a rocket. If the asteroid was discovered too late to deflect it away from the earth, we may try to completely vaporise it, with ever more powerful nuclear detonation. A Hail Mary approach, that risks turning the cannonball into a now radioactive shotgun spray."

Dr. Robin George Andrews, journalist and author, was talking on an episode of BBC Inside Science.

The references to cannonballs and shot from guns can be seen as an extended metaphor. ('Punch' is also a metaphor here.)

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The reference to the asteroid being like a rocket (as it is propelled by the emission of some of its own material) is a simile.

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To describe vaporising the asteroid as a Hail Mary approach is to employ an idiom where the meaning is only obvious to someone who is aware of the idiomatic use of the term.

Read about communicating science through idioms

rupture of crust is like fracturing a long bar of steel

An analogy used in maing a scientific argument:

"…we know that eruptions on an enormous scale have happened through old vents, even in areas subject to far-extended and undulating earthquakes, without such movements having been produced. From this consideration, and from the fact that the force of earthquakes appears to have a definite relation to the thickness of crust ruptured, as we may conclude from the great difference in the effects caused by an eruption through an old, and one through a new orifice, I do not conceive we are justified in admitting the hypothesis of an undulating fluid. The two kinds of movements may, possibly, be explained, by considering that when the crust yields to the tension, caused by its gradual elevation, there is a jar at the moment of rupture, and a greater movement may be produced by the tilting up of the edges of the strata and by the passage of the fluid rock between them. In breaking a long bar of steel, would not a jar be caused by the fracture, as well as a vibration of the two ends when separate?"

Charles Darwin, 1840, On the connexion of certain volcanic phenomena in South America; and on the formation of mountain chains and volcanos, as the effect of the same powers by which continents are elevated. (Transactions of the Geological Society of London)

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volcanos send up columns of smoke like signals of a new period of violence

An example of simile used in science writing:

"We have, also, seen that, when the island of Chiloe was strongly shaken, some men at work on the flanks of the Cordillera, between the volcanos of Osorno and Minchinmadom, (which both sent up dark columns of smoke, like signals to mark the new period of violence,) were quite unaware of the great convulsion, which then caused the shores of the Pacific to vibrate throughout a space of more than a thousand miles."
Charles Darwin, 1840, On the connexion of certain volcanic phenomena in South America; and on the formation of mountain chains and volcanos, as the effect of the same powers by which continents are elevated. (Transactions of the Geological Society of London)

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Note: when volcanoes "sen[d] up dark columns of smoke", this can certainly be read as a sign of a possible "new period of violence"; however clearly the volcanos are not sending up the smoke as signals. To read these signs as (intended) signals would be to amthropomorphise the volcanos.

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

Andes is one great wall

An example of metaphor in science writing:

"To illustrate the case: if we suppose Stromboli and Vesuvius to be in violent eruption on the same hour of the night, little would be thought of the coincidence; but it would be otherwise if this should happen with Vesuvius and Etna; and our surprise would be greatly increased if we afterwards heard that Hekla, after twenty-six years' repose, had burst forth at the same time with tremendous explosions. Nevertheless, if such a coincidence had occurred in Europe, a country possessing no unity of character, and the two points not being more than 2000 miles apart, it is very doubtful how far the phenomenon would have been worthy of consideration. But the case is different in America, where the volcanic orifices all fall on one great wall or fissure, (for the Andes may be indifferently so called,) and where the immensity of the level area on the eastern side, proves with what wonderful equability the subterranean forces have acted on this portion of the globe."

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in earthquakes weak spasms precede the worst convulsions

An example of an extended metaphor in science writing:

"This eruption, probably, was the first indication of those great volcanic disturbances which ensued exactly one month afterwards; for it seems to be a very general occurrence in earthquakes, that weak spasms precede the worst convulsions."

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crust of earth is like a thin sheet of ice over a frozen pool

An example of an analogy used to explain a scientific hypothesis:

When first considering these phenomena, which prove that an actual movement in the subterranean volcanic matter occurred almost at the same instant of time at very distant places, the idea of water splashing up through holes in the ice of a frozen pool, when a person stamps on the surface, came irresistibly before my mind. The inference from it was obvious, namely, that the land in Chile floated on a lake of molten stone, of which the area, as known from the various points in eruption on the day of the earthquake, would be nearly double that of the Black Sea. If this inference be denied, the only alternative is, that channels from the various points of eruption unite in some deep-seated focus, like the arteries of the body in the heart, whence an impulse can be transmitted to distant parts of the surface, with nearly equal force. But according to this view, if two separate trains of volcanos in the Andes have any connexion whatever, which seems highly probable from the symmetry of the Cordillera, (and possibly an intimate one, as will presently be discussed,) then the common focus, from which the two main branches are sent off, must be seated at an enormous depth. But all the calculations regarding the depth at which molten rocks must necessarily be met with, if they can be at all trusted, tend to prove, that the earth's crust is not much more, and perhaps less, than twenty miles in thickness; and if this be so, the crust may, indeed, be well compared with a thin sheet of ice over a frozen pool…

The motion of the earth, on February 20th, 1835, at Valdivia, appeared to me like that of a crust, spread over an undulating fluid; and in my Journal, I have compared the motion to the bending of thin ice, beneath a moving weight. Afterwards, when I became convinced that the crust there does rest upon a sea of molten rock, my first impression regarding the movement was strongly confirmed."

Darwin offers two analogies here. Firstly the idea of crust-molten rock compared to ice-pool, extended to how volcanic erruptions could be like water splashing out of holes in the ice. His second suggestion (which he argues againts) has the cannels bringing magma from a common underground source as like arteries (bringing blood) from the heart.

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