by Guy Murchie
Now consider the moon, which after all seems not so different from the balloon when passing overhead for she subtends the same angle of half a degree and the average person (according to surveys) subconsciously thinks of her as only a few hundred feet up and moving across what appears to be the shallow but wide vault of the sky. Yet the moon does not behave like a normal balloon because she does not dwindle when approaching the far horizon. Instead she behaves just like the miracle balloon that somehow failed to diminish with distance, so your conditioned mind tends to assure you that the moon also must be swollen to look so big while yet so remote. In this case of course, your mind, despite its habit of compensating, should not (under reason) do so since the moon's overhead distance (about 240,000 miles and far too much for the mind to grasp) remains practically the same at the horizon, holding its subtended angle within two percent of constancy. And you tend to forget that the moon is not just twice or ten times farther away than the hills on the horizon but actually 25,000 times farther away. So, out of habit and an eminently natural misjudgment of the apparent dome of the sky, the experienced mind (of man or animal) under such circumstances cannot help but compensate. In fact the mind clearly overcompensates by bloating the moon to three times her actual size, somewhat as a drug addict's nerves (having learned to compensate for heroin) overcompensate agonizingly when the heroin is withheld.
Other illusions are now understood to work for similar reasons, the mind unreasoningly compensating (often overcompensating) according to its long-accustomed perspectives, as you see in these drawings. Lines converging upward, for example, are apt to be interpreted by the conditioned brain as parallel and receding like railroad rails so that a line drawn crosswise between them looks longer when higher because the brain automatically accepts it (like the moon on the horizon) as farther off and reaching almost from "rail" to "rail" instead of less than halfway as in the case of a lower (apparently nearer) line. Indeed it is a cardinal rule of illusion that when two objects are optically equal in size (subtending equal angles at the observer's eye), the one that appears to be farther away will thereby seem proportionately larger.
Also, because we move mostly through horizontal landscapes, vertical lines make a greater visual impact on us and, in consequence, generally appear longer than equal horizontal lines - which explains this famous top hat illusion, where the crown seems to rise almost a third taller than the equal width of the brim.
Wavy lines resembling hair also give the illusion of movement, and a white lattice seen against a black background elicits little gray ghosts at the intersections where brightness (induced by dark contrast) is minimal - all such impressions presumably arising from what an engineer might call information-processing mechanisms in the brain that, under more usual circumstances, make the visible world easier to comprehend. The fact that one has a self and a local point of view of course accounts for many common illusions: the house rolling rearward as you gallop past it on your horse, the tree swinging into the road, the sun setting, the moon sailing through branches, the tower falling past the clouds ...
Illusions occur in all the senses more or less, and, since all senses (like all things) are related, they often overlap or merge into one another. You may have noticed that, when you heft two objects equal in weight but different in size, the smaller one always seems the heavier because you expected it to be lighter. It is a case of errant subconscious compensation. Or, in homelier terms, when pints presume to speak in pounds, their language is liable to be misunderstood. Another significant type of illusion was devised in 1832 by L. A.
Necker, a Swiss naturalist, who drew a transparent cube on a piece of paper and noticed that its perspective had a strange way of reversing itself, as the face that seemed to be in front would suddenly flip to the back in exchange for the back face's seeming to flip to the front. Although a shift in eye fixation or a mental effort could induce this exchange in perception, Necker discovered it would also happen quite spontaneously every few seconds. And he designed a pair of weird "boxes" that, as you can see, flip even faster. Evidently the fact that such a two-dimensional image representing a three-dimensional object is ambiguous and offers two possible interpretations as to what it represents makes the brain search for the true answer to the paradox by trying out the hypotheses alternately and never conclusively settling on either. And something similar occurs in the case of other so-called impossible objects, like the accompanying ambiguous triangle and endless stair on which you can mentally walk up clockwise or down counterclockwise, round and round, forever without getting anywhere.
THE VISIBILITY-INVISIBILITY SENSE
Naturally illusions have been a factor in evolution by helping creatures deceive their prey or their predators, and so they introduce us to the passive side of the sense of sight, which takes two almost opposite forms: (1) the introverted sense of self-visibility with which one may increase one's conspicuousness, like a peacock advertising his masculinity to woo a mate or a cat hunching his back to unnerve a dog. Or (2) the reciprocal sense of self-invisibility with which one may decrease one's conspicuousness through camouflage in uncounted ways, some of them so fantastic that few humans are yet aware of them.
Most obvious among forms of camouflage is the relatively simple principle of concealment by hiding that includes tactics such as the smokescreen of the squid who, when attacked, spews out either a black squid-sized cloud near the sea's surface or a blindingly luminous trail in the inky depths. A more subtle way is to make your body match its background by some such method as shifting skin pigments as the chameleon does. Or, in the case of some leaf-eating insects, having a transparent body, so that the eaten leaves inside you show through, automatically keeping you the same color as the similar uneaten leaves you are living on. And at least one ambitious caterpillar in South America, apparently unwilling to conform to his surroundings, contrives to make his surroundings conform to him - achieving this "miracle" by carving his own image in every leaf he eats, carefully forgoing just enough of certain parts of the leaf so that, after he has been feeding a few hours in a tree, it has begun to look like a tree full of caterpillars - a stratagem understandably frustrating to the hungry birds.
Slightly different is disruptive camouflage, in which concealment depends on breaking up an animal's outline with contrasting patches or stripes, like those on a zebra which could disguise him slightly if they ran lengthwise along his body but do a lot better by cutting across it. Or if you wonder how a tropical frog wearing a gaudy yellow stripe across his back from right cheek to left leg can afford to attract such attention to himself, you are overlooking the fact that the yellow stripe not only bears no resemblance to the real frog but looks from a little distance like a dry twig or a wilted blade of grass and, in the frog's natural setting, helps to conceal him.
Obliterative shading is another technique in which the normal contrast between sunlit upper surfaces and shadowy underparts of creatures is canceled by darkening their backs and lightening their bellies (in some deep-sea fish with luminescence) to camouflage them. And shadow elimination is an aspect of it by which a butterfly, say, rests with his wings together and aligned exactly edge-on to the sun so they cast no telltale shadow. These methods are also used by human camoufleurs to countershade big guns, rocket launchers, etc., eliminating their shadows with netting and even enticing bombers to drop their bombs off target by erecting huge sheets of composition board cut to cast shadows like those of important buildings designated for destruction but actually disguised and a safe distance away.
The eye is a conspicuous organ, not only inclined to be big, round and shiny, but it functions best when fairly exposed to view, so naturally it has provoked its own rather special camouflage adaptations during evolution. Some vipers, for instance, hide the eye by having an iris that matches the rest of them, while the vital pupil remains (in daylight) only a tiny slit. Certain reptiles have transparent but lacy eyelids through which they can keep a semiwatch with restricted, inconspicuous v
ision until they are spotted. Many creatures disguise the eye with a dark stripe of nearly the iris color and a few, like the butterflies, divert attention with big scary fake eyes on their wings. There is also the stripe-eyed butterfly fish that, like a butterfly, has two perfect eye spots near his tail, giving the impression that that is his head end, an effect heightened by his habit of swimming slowly backward - the performance really paying off when some marauder tries to head him off by lunging at what seems a vital Spot, only to be foiled when he unexpectedly darts away in the opposite direction.
A good deal of animal camouflage is thus mixed with advertising, making use of the pickpocket's notorious distraction principle of having an accomplice bump provocatively into the victim's opposite side while he himself is gently lifting his wallet, a dodge that could have been suggested by the lizard's detachable tail that separates neatly when the animal is closely pursued, duping the voracious pursuer by continuing to writhe and slither in one direction while the rest of the lizard escapes in another to start growing a new tail. In some cases similar display-camouflage is used to lure prey to the business end of a predatory animal, say an angler fish with its luminous bait (pages 30 - 31).
In other cases the disguise may advertise the genuine inedibility of an animal known to predators as nasty tasting, or it may seek safety through pretended inedibility by mimicking such a creature. One caterpillar, to avoid being eaten, goes so far as to look as if he's already been eaten and disgorged - you know: that thrown-up look - while a certain Indian mantis pretends to be newly squashed and therefore not worth eating. The hunted animal may even flash a warning to his pursuer to look out for a really dangerous defense weapon, like the terrible-looking black dorsal fin of the tasty weever fish with its two poisonous spikes, the mere sight of which spares both him and most of his opponents a lot of unpleasantness. And of course there is no end to sham warnings like those of the bluffing South American fulgorid, a large insect with false teeth and fake eyes in a preposterous yet often successful attempt to palm himself off as the head of a ferocious young alligator.
Surely the most extraordinary of all such make-believery, however, is the construct of a Malaysian spider faced with the tantalizing double problem of avoiding being eaten by birds while attracting flies to his web - a defense-offense challenge he manages to meet with a single dramatic act that I can only appraise as exhibiting practical but divine imagination. The spider's black and white body, you see, is designed to look exactly like the solid lump of a bird's dropping, and he spins his whitish web with flat lobes extending in several directions upon some large leaf to resemble the splash so often associated with this kind of excrement, the effect being augmented by the faint ammoniac odor of the spider's own exudations. And the act is surprisingly successful, for the last thing a bird wants to eat is one of his own droppings, while it is hard to think of anything more attractive to the flies as they buzz toward the web in eager swarms.
Comparing visibilities correctly of course takes an artist's eye for color, and resistance to the common tendency to think of snow as white and grass as green, when both may actually be reflecting subtle shades of blue or lavender. And allowance is needed for the differing values of colors as seen by different eyes. The ancient Greeks, for instance, had no word for blue, while the Natchez Indians failed to distinguish between green and yellow, and the Choctaws between green and blue. Most fish and birds, however, can see red and some greens, but probably little if any blue, while bees see ultraviolet but not red, and green to them may look yellow. Hardly any mammals except man and his close relatives see color of any sort, yet the bee evidently notices contrasting hues even within the narrow waveband of what appears to us as white, and, as for night creatures, they naturally specialize in the dark-penetrating frequencies called infrared.
Colors also influence minds and moods, probably more than is generally recognized, and color engineers say their research shows that violet in clothes or home decoration induces melancholy, while yellow is an energizing color that stimulates thought, conviviality and optimism. Contrary to tradition, blue does not really give you "the blues" but rather relaxes you. In fact old people can become "blue thirsty," presumably because their yellowing eye fluids filter out blue light, which seems to make some of them crave blue, like a nostalgia for carefree youth. Color produces its own illusions, making a red house appear some five percent closer than an equidistant blue house, or a pale yellow suitcase pounds (as well as shades) lighter than a dark blue one of the same weight. And while customers in a bar painted red seem to get thirstier and buy more drinks than people in any cooler-colored bar, an appeal for charity mailed in a light blue-green envelope has been found to bring a consistently more generous response than the same appeal in a white envelope. There is even a suggestion that this sort of color control may have been a factor in football history, for the famous Knute Rockne is reported to have regularly kept his Notre Dame team keyed up in a red locker room while consigning visiting rivals to one tinted a soporific blue.
RADIATION SENSE
Now we must consider the parts of the radiation spectrum beyond visible light, which means radiation of wavelengths shorter than violet on one hand and longer than red on the other. The waves just beyond violet are called ultraviolet, and the first creature I can think of with senses in this range is the bee, who sees ultravioletly very well and is known to respond to the bright petals of the many flowers that flash rings of this radiation so alluringly they are virtually impossible for him to resist. If a bee were on the moon, which obviously could happen in this age of space travel, his view of the crescent Earth, in case you're interested, might look something like this ultraviolet picture of our planet taken by his human cousin on the moon in 1972.
When it comes to the radiation of waves shorter than ultraviolet, like x- and gamma rays, or longer than infrared, like radar and the broadcasting bands of radio and television, few people seem to realize how naturally most earthly creatures sense them. Indeed there appears to be a general impression that these waves were invented by man and brought into the world only in the last hundred years. But the fact is that, far from being invented by man, these reaches of radiation were only discovered by him, for they are actually timeless parts of the great radiation spectrum that is a fundamental aspect of the universe. It is a spectrum, by the way, in which color (light wave frequency) corresponds to pitch (sound wave frequency) and all of its seventy known octaves (69 of them invisible) are beautifully analogous to music.
A case in point was the research done in the U.S. Naval Radiological Defense Laboratory in San Francisco in the 1960s in which sleeping rats were exposed to 250,000-volt x-rays. This sort of radiation had always been regarded as silent, invisible and unfeelable, but every time it was beamed on the rats, their heartbeats began to accelerate and within fifteen seconds they woke up, sometimes in a state of alarm. Again, when the animals were offered their favorite drink, sweetened water, while exposed to radiation, they couldn't swallow it. Even humans, it was discovered, can sense short-wave radiation when their eyes are adapted to darkness, for night vision somehow sensitizes their retinal rod cells to the point where they see both x-rays and gamma rays as a yellowish-green glow, accompanied sometimes by a tingling or burning sensation. And in the rare cases of runaway nuclear reactors when someone is subjected to massive lethal radiation, he usually tells of seeing a "vivid blue flash," even in sunlight, which unhappily amounts to an irreprievable sentence of death only hours away.
Long-wave radiation is much gentler, but has nevertheless yielded evidence of being naturally perceptible under certain circumstances. The New England Institute for Medical Research in Ridgefield, Connecticut, for instance, found in 1958 that pulsed radio waves (5 to 40 megacycles) could regiment many organic substances such as carbon, starch, red blood cells and even organisms like amebas, euglenas and paramecia which tend to align themselves and swim along the invisible lines of force of the radiating field, sometimes practically dancing
to music. Although humans appear to need the aid of some form of metal or crystal in order to tune in to radio or TV waves, this doesn't always require much of a receiver, to judge by the innumerable reported cases of people who hear music or messages coming from tooth fillings, bridgework, bobby pins and steam radiators. A man in New Jersey with a mouthful of dental work wrote, "I've been getting Station WOR regularly." And inasmuch as bones, muscles and other parts of the body are crystalline in structure, to say nothing of trees and rocks, who knows what or who will be heard from next?
TEMPERATURE SENSE
Awareness of temperature is commonly considered part of the sense of feeling because one feels it. But it is really more logical to classify it as a radiation sense, akin to vision, because it is a tuning in on radiation - in this case infrared radiation, commonly called heat. That is why I turn to the temperature sense now, following most of the other radiation senses. It is a vital sense too, often protecting an organism against dangerous overheating or freezing. And it makes possible man's extraordinary range of heat tolerance, through which, I am told, naked airmen tested in dry air in 1960 set a world record by withstanding temperatures up to 400°F. and heavily clothed men to more than 500°F., while in the steamy atmosphere of a sauna bath some described 284°F. as "quite bearable" despite its being 72° above the boiling point of water.