Read The Faber Book of Science Online
Authors: John Carey
Sir Isaac Newton (1642–1727), ‘one of the tiny handful of supreme geniuses who have shaped the categories of the human intellect’ (in the words of his biographer, Richard S. Westfall), was born into an entirely undistinguished, semi-literate sheep-farming family in rural Lincolnshire. His youthful encounter with an apple is the best known of all scientific stories, and, surprisingly, seems to be true. Dr William Stukeley, who knew Newton well in his old age, records:
On 15 April 1726 I paid a visit to Sir Isaac at his lodgings in Orbels Buildings in Kensington, dined with him, and spent the whole day with him, alone …
After dinner, the weather being warm, we went into the garden and drank tea, under the shade of some apple trees, only he and myself. Amidst other discourse, he told me he was just in the same situation as when, formerly, the notion of gravitation came into his mind. It was occasioned by the fall of an apple, as he sat in a contemplative mood. Why should that apple always descend perpendicularly to the ground, thought he to himself? Why should it not go sideways or upwards, but constantly to the earth’s centre? Assuredly, the reason is, that the earth draws it. There must be a drawing power in matter: and the sum of the drawing power in the matter of the earth must be in the earth’s centre, not in any side of the earth. Therefore does this apple fall perpendicularly, or towards the centre. If matter thus draws matter, it must be in proportion of its quantity. Therefore the apple draws the earth, as well as the earth draws the apple. That there is a power, like that we here call gravity, which extends itself through the universe.
And thus by degrees he began to apply this property of gravitation to the motion of the earth and of the heavenly bodies, to consider their distances, their magnitudes and their periodical revolutions; to find out that this property, conjointly with a progressive motion impressed on them at the beginning, perfectly solved their circular courses; kept
the planets from falling upon one another, or dropping all together into one centre; and thus he unfolded the universe. This was the birth of those amazing discoveries, whereby he built philosophy on a solid foundation, to the astonishment of all Europe.
Asked at an earlier stage in his life how he had discovered the law of universal gravitation, Newton had replied ‘By thinking on it continually’ – a remark that supplements, but does not contradict, Stukeley’s apple story.
Newton’s law, set out in the
Principia
(1687), states that every particle of matter in the universe attracts every other particle with a force that varies according to its mass and to the inverse square of the distance between them. This remained the accepted explanation of gravity until it was superseded by Einstein’s theory of general relativity in 1915 (see p. 267, below).
Newton’s other great scientific work was the
Optics,
not published till 1704, but based on experiments he made as a young man at Cambridge to discover the nature of light:
In a very dark chamber, at a round hole, about one third part of an inch broad, made in the shut [shutter] of a window, I placed a glass prism, whereby the beam of the sun’s light, which came in at that hole, might be refracted upwards towards the opposite wall of the chamber, and there form a coloured image of the sun …
So began Newton’s account of his experiments with prisms, which led him to the discovery that ordinary white light is really a mixture of rays of every variety of colour. He found, too, that the ray of each colour bends at a certain definite angle on passing through the prism – red being the least bendable, followed by ‘orange, yellow, green, blue, indigo, deep violet’. The richness of his response to colour is evident in his experimental accounts, as here where he is explaining that a ray of a single (or ‘homogeneal’) colour, shining upon objects, makes them all appear of that colour:
All white, grey, red, yellow, green, blue, violet bodies, as paper, ashes, red lead, orpiment, indigo bice [dark blue], gold, silver, copper, grass, blue flowers, violets, bubbles of water tinged with various colours, peacock’s feathers, the tincture of
lignum
nephriticum
[a wood imported from Spain, the blue infusions of which were used for kidney-disease], and suchlike, in red homogeneal light appeared totally red, in blue light totally blue, in green light totally green, and so of other colours. In the homogeneal light of any colour they all
appeared totally of that same colour, with this only difference, that some of them reflected that light more strongly, others more faintly. I never yet found any body, which by reflecting homogeneal light could sensibly change its colour.
From all which it is manifest that if the sun’s light consisted of but one sort of rays, there would be but one colour in the whole world.
Newton’s friend Edmond Halley (observer of ‘Halley’s Comet’) had engaged in underwater operations off the Sussex coast in a diving bell, and conversation with him enables Newton to draw imaginative conclusions about underwater colours:
Mr Halley, … in diving deep into the sea in a diving vessel, found in a clear sunshine day that, when he was sunk many fathoms deep into the water, the upper part of his hand, on which the sun shone directly through the water and through a small glass window in the vessel, appeared of a red colour, like that of a damask rose, and the water below and the under part of his hand, illuminated by light reflected from the water below, looked green. For thence it may be gathered that the sea-water reflects back the violet and blue-making rays most easily, and lets the red-making rays pass most freely and copiously to great depths. For thereby the sun’s direct light at all great depths, by reason of the predominating red-making rays, must appear red.
Newton’s theory that white light was not pure but a medley of different colours met with strong opposition. It seemed counter to common sense, which had long associated whiteness with purity and simplicity. Poets, however responded to the new colour-theory excitedly. The influence of the
Optics
flooded eighteenth-century poetry with colour. Alexander Pope’s ‘sylphs’ – fairy creatures who flit around a young lady’s dressing-table in his poem
The
Rape
of
the
Lock
– show clear evidence of Newton’s prismatic discoveries:
Transparent forms, too fine for mortal sight,
Their fluid bodies half-dissolved in light.
Loose to the wind their airy garments flew,
Thin glittering textures of the filmy dew;
Dipped in the richest tincture of the skies,
Where light disports in ever-mingling dyes,
While every beam new transient colours flings,
Colours that change whene’er they wave their wings
Later, however, in reaction against eighteenth-century Enlightenment values, the Romantic poets condemned Newton for banishing mystery from the universe, and reducing everything to fact and reason. ‘Art is the Tree of Life. Science is the Tree of Death,’ proclaimed William Blake. John Keats agreed that Newton had ‘destroyed all the poetry of the rainbow by reducing it to prismatic colours’ – an opinion he versified in
Lamia:
There was an awful rainbow once in heaven;
We know her woof, her texture; she is given
In the dull catalogue of common things.
Philosophy will clip an angel’s wings,
Conquer all mysteries by rule and line …
These Romantic outbursts suggest a profound ignorance of Newton, who was, in fact, acutely aware of the mystery of the universe. Colour itself, he points out in the
Optics,
is mysterious. What we call ‘colour’ in an object is merely ‘a disposition to reflect this or that sort of rays more copiously than the rest’, and the rays themselves are not really ‘coloured’, but set up a motion that, when it meets our eye, gives us the sensation of colour – ‘as sound in a bell or musical string, or other sounding body, is nothing but a trembling motion’. Why particular objects should reflect particular rays, and how they affect the eye to suggest colours, Newton found inexplicable.
In the twentieth century Alfred North Whitehead rephrased this problem, and its implications for poets, in his
Science
and
the
Modern
World
:
There is no light or colour as a fact in external nature. There is merely motion of material. Again, when the light enters your eyes and falls on the retina, there is merely motion of material. Then your nerves are affected and your brain is affected, and again this is merely motion of material … The mind, in apprehending, experiences sensations which, properly speaking, are qualities of the mind alone. These sensations are projected by the mind so as to clothe appropriate bodies in external nature. Thus the bodies are perceived as with qualities which in reality do not belong to them, qualities which in fact are purely the offspring of the mind. Thus nature gets credit which should in truth be reserved for ourselves: the rose for its scent; the nightingale for his song; and the sun for his radiance. The poets are entirely mistaken. They should address their lyrics to themselves.
How little Newton’s discoveries had diminished his sense of mystery, he himself explained not long before his death:
I don’t know what I may seem to the world, but, as to myself, I seem to have been only like a boy playing on the sea shore, and diverting myself in now and then finding a smoother pebble or a prettier shell than ordinary, whilst the great ocean of truth lay all undiscovered before me.
Sources: William Stukeley,
Memoirs
of
Sir
Isaac
Newton’s
Life,
1752. Sir Isaac Newton,
Optics,
1704. A. N. Whitehead,
Science
and
the Modern World
,
Cambridge, Cambridge University Press, 1926.
Gilbert White (1720–93) was the first great English field naturalist. A country parson, he spent virtually all his life in the Hampshire village of Selborne, and his letters to two fellow naturalists about the local fauna and flora were published in 1788 as
The
Natural
History
of
Selborne.
Among the British species that he was the first to identify was the little red mouse or harvest mouse (
Micromys
minutus
.)
I have procured some of the mice mentioned in my former letters, a young one and a female with young, both of which I have preserved in brandy. From the colour, shape, size, and manner of nesting, I make no doubt but that the species is nondescript [not previously identified]. They are much smaller and more slender than the
mus
domesticus
medius
of Ray; and have more of the squirrel or dormouse colour: their belly is white, a straight line along their sides divides the shades of their back and belly. They never enter into houses; are carried into ricks and barns with the sheaves; abound in harvest, and build their nests amidst the straws of the corn above the ground, and sometimes in thistles. They breed as many as eight at a litter, in a little round nest composed of the blades of grass or wheat.
One of these nests I procured this autumn, most artificially platted, and composed or the blades of wheat; perfectly round, and about the size of a cricket-ball; with the aperture so ingeniously closed, that there was no discovering to what part it belonged. It was so compact and well filled, that it would roll across the table without being discomposed, though it contained eight little mice that were naked and blind. As this nest was perfectly full, how could the dam come at her litter respectively so as to administer a teat to each? Perhaps she opens different places for that purpose, adjusting them again when the business is over: but she could not possibly be contained herself in the
ball with her young, which moreover would be daily increasing in bulk. This wonderful procreant cradle, an elegant instance of the efforts of instinct, was found in a wheat-field, suspended in the head of a thistle …
As to the small mice, I have farther to remark, that though they hang their nests for breeding up amidst the straws of the standing corn, above the ground; yet I find that, in the winter, they burrow deep in the earth, and make warm beds of grass: but their grand rendezvous seems to be in corn-ricks, into which they are carried at harvest. A neighbour housed an oat-rick lately, under the thatch of which were assembled near an hundred, most of which were taken; and some I saw. I measured them; and found that, from nose to tail, they were just two inches and a quarter, and their tails just two inches long. Two of them, in a scale, weighed down just one copper halfpenny, which is about a third of an ounce avoirdupois: so that I suppose they are the smallest quadrupeds in this island. A full-grown
mus
medius
domesticus
weighs, I find, one ounce, lumping weight, which is more than six times as much as the mouse above; and measures from nose to rump four inches and a quarter, and the same in its tail.
… As my neighbour was housing a rick he observed that his dogs devoured all the little red mice that they could catch, but rejected the common mice: and that his cats ate the common mice, refusing the red …
*
There is a steep abrupt pasture field interspersed with furze close to the back of this village, well known by the name of the Short Lithe, consisting of a rocky dry soil, and inclining to the afternoon sun. This spot abounds with the
gryllus
campestris
, or field-cricket; which, though frequent in these parts, is by no means a common insect in many other counties.
As their cheerful summer cry cannot but draw the attention of a naturalist, I have often gone down to examine the œconomy of these
grylli
, and study their mode of life: but they are so shy and cautious
that it is no easy matter to get a sight of them; for, feeling a person’s footsteps as he advances, they stop short in the midst of their song, and retire backward nimbly into their burrows, where they lurk till all suspicion of danger is over.
At first we attempted to dig them out with a spade, but without any great success; for either we could not get to the bottom of the hole, which often terminated under a great stone; or else, in breaking up the ground, we inadvertently squeezed the poor insect to death. Out of one so bruised we took a multitude of eggs, which were long and narrow, of a yellow colour, and covered with a very tough skin. By this accident we learned to distinguish the male from the female; the former of which is shining black, with a golden stripe across his shoulders; the latter is more dusky, more capacious about the abdomen, and carries a long sword-shaped weapon at her tail, which probably is the instrument with which she deposits her eggs in crannies and safe receptacles.
Where violent methods will not avail, more gentle means will often succeed; and so it proved in the present case; for, though a spade be too boisterous and rough an implement, a pliant stalk of grass, gently insinuated into the caverns, will probe their windings to the bottom, and quickly bring out the inhabitant; and thus the humane inquirer may gratify his curiosity without injuring the object of it. It is remarkable that, though these insects are furnished with long legs behind, and brawny thighs for leaping, like grasshoppers; yet when driven from their holes they show no activity, but crawl along in a shiftless manner, so as easily to be taken: and again, though provided with a curious apparatus of wings, yet they never exert them when there seems to be the greatest occasion. The males only make that shrilling noise perhaps out of rivalry and emulation, as is the case with many animals which exert some sprightly note during their breeding time: it is raised by a brisk friction of one wing against the other. They are solitary beings, living singly male or female, each as it may happen: but there must be a time when the sexes have some intercourse, and then the wings may be useful perhaps during the hours of night. When the males meet they will fight fiercely, as I found by some which I put into the crevices of a dry stone wall, where I should have been glad to have made them settle. For though they seemed distressed by being taken out of their knowledge, yet the first that got possession of the chinks would seize upon any that were obtruded upon them with a
vast row of serrated fangs. With their strong jaws, toothed like the shears of a lobster’s claws, they perforate and round their curious regular cells, having no fore-claws to dig, like the mole-cricket. When taken in hand I could not but wonder that they never offered to defend themselves, though armed with such formidable weapons. Of such herbs as grow before the mouths of their burrows they eat indiscriminately; and on a little platform, which they make just by, they drop their dung; and never, in the day-time, seem to stir more than two or three inches from home. Sitting in the entrance of their caverns they chirp all night as well as day from the middle of the month of May to the middle of July; and in hot weather, when they are most vigorous, they make the hills echo; and, in the stiller hours of darkness, may be heard to a considerable distance. In the beginning of the season, their notes are more faint and inward; but become louder as the summer advances, and so die away again by degrees.
Sounds do not always give us pleasure according to their sweetness and melody; nor do harsh sounds always displease. We are more apt to be captivated or disgusted with the associations which they promote, than with the notes themselves. Thus the shrilling of the field-cricket, though sharp and stridulous, yet marvellously delights some hearers, filling their minds with a train of summer ideas of everything that is rural, verdurous, and joyous.
About the tenth of March the crickets appear at the mouths of their cells, which they then open and bore, and shape very elegantly. All that ever I have seen at that season were in their pupa state, and had only the rudiments of wings, lying under a skin or coat, which must be cast before the insect can arrive at its perfect state (We have observed that they cast these skins in April, which are then seen lying at the mouths of their holes.) From whence I should suppose that the old ones of last year do not always survive the winter. In August their holes begin to be obliterated, and the insects are seen no more till spring.
Not many summers ago I endeavoured to transplant a colony to the terrace in my garden, by boring deep holes in the sloping turf. The new inhabitants stayed some time, and fed and sung; but wandered away by degrees, and were heard at a farther distance every morning; so that it appears that on this emergency they made use of their wings in attempting to return to the spot from which they were taken.
One of these crickets, when confined in a paper cage and set in the sun, and supplied with plants moistened with water, will feed and
thrive, and become so merry and loud as to be irksome in the same room where a person is sitting: if the plants are not wetted it will die.
White is still quoted as an authority on the field cricket in some
twentieth-century
works on entomology. During the Second World War, as a prisoner of war in Bavaria, R. D. Purchon made a study of the field cricket which confirmed White’s observations. Purchon found that the adult crickets die in August, and the young ones continue active until late autumn, when they hibernate in their pupa state.
Source: Gilbert White,
The
Natural
History
of Selbourne,
1788.