The Faber Book of Science

by John Carey

  When seventeenth-century poets thought of the human body they still thought of Vesalius’ anatomy pictures and executed criminals, as this extract from Andrew Marvell’s Dialogue between the Soul and Body suggests. Like Vesalius, Marvell considers the heart ‘double’, formed only of the two ventricles. Vesalius regarded the right atrium as a passageway for the vena cava, and the left as part of the pulmonary vein.

  O who shall from this dungeon raise

  A soul enslaved so many ways? …

  A soul hung up, as ’twere, in chains

  Of nerves and arteries and veins.

  Tortured, besides each other part,

  In a vain head and double heart.

  Sources: Vesalius translation (slightly altered) from Andreas Vesalius’ First Public Anatomy at Bologna, 1540. An Eyewitness Report By Baldasar Heseler, ed. Ruben Eriksson, Uppsala and Stockholm, Almquist & Wiksells Boktryckeri AB, 1959.

  Galileo and the Telescope

  Until the sixteenth century the accepted model of the universe was that developed by the second-century Alexandrian astrologer Ptolemy. According to this, the sun and the planets revolved round the earth. Over the centuries, complex adjustments were added to Ptolemy’s system to make it fit astronomical observations.

  The Pole Nicolaus Copernicus (1473–1543), a canon of the cathedral church at Frauenberg, and an amateur astronomer, put forward the hypothesis (in his book On the Revolutions of the Heavenly Spheres, published in 1543) that the earth moved, and went round the sun, which remained stationary. This contradicted several biblical texts, for example Joshua 10: 12–13, where Joshua commands the sun to stand still, implying that it normally moves. However the Church did not object. Copernicus dedicated his work to Pope Paul III and a cardinal and a bishop were among friends who urged him to publish. His theory was regarded as a harmless mathematical speculation. Most people did not take it seriously. Martin Luther spoke for the general public: ‘This fool wishes to reverse the entire science of astronomy, but sacred scripture tells us that Joshua commanded the sun to stand still, and not the earth.’

  With the advent of the telescope, however, observation replaced theory, and the old map of the heavens could be shown to be false. The inventor of the telescope is not known, but it was probably an obscure Dutch spectacle-maker living in Middelburg, Hans Lippershey. There is a story that, around 1600, two children were playing with lenses in his shop and found that by holding two together they could magnify the church weathervane. This led him to construct a simple telescope. By 1609 telescopes, under the name of ‘Dutch trunks’, were being made and sold in several European cities, including Venice, Padua, Paris and London.

  Galileo Galilei (1564–1642) was a skilful instrument-maker and Professor of Mathematics at Padua University. To eke out his meagre salary, he kept a small shop in Padua, selling scientific instruments. About May 1609, he heard about telescopes and began constructing them. They were regarded as chiefly useful for observation on land or at sea. But it occurred to him to look at the sky through one. He published the astonishing results in March 1610 in a 24-page pamphlet called The Starry Messenger (Siderius Nuncius). It was written in a tersely factual style no scholar had used before, and it fell like a bombshell on the learned world.

  About ten months ago a report reached my ears that a Dutchman had constructed a telescope, by the aid of which visible objects, although at a great distance from the eye of the observer, were seen distinctly as if near; and some proofs of its most wonderful performances were reported which some gave credence to, but others contradicted. A few days after, I received confirmation of the report in a letter written from Paris by a noble Frenchman, Jaques Badovere, which finally determined me to give myself up first to inquire into the principle of the telescope, and then to consider the means by which I might compass the invention of a similar instrument, which a little while after I succeeded in doing, through deep study of the theory of Refraction; and I prepared a tube, at first of lead, in the ends of which I fitted two glass lenses, both plane on one side, but on the other side one spherically convex, and the other concave. Then bringing my eye to the concave lens I saw objects satisfactorily large and near, for they appeared one-third of the distance off and nine times larger than when they are seen with the natural eye alone. I shortly afterwards constructed another telescope with more nicety, which magnified objects more than sixty times. At length, by sparing neither labour nor expense, I succeeded in constructing for myself an instrument so superior that objects seen through it appear magnified nearly a thousand times, and more than thirty times nearer than if viewed by the natural powers of sight alone.

  It would be altogether a waste of time to enumerate the number and importance of the benefits which this instrument may be expected to confer, when used by land or sea. But without paying attention to its use for terrestrial objects, I betook myself to observations of the heavenly bodies; and first of all, I viewed the Moon as near as if it was scarcely two semi-diameters of the Earth distant. After the Moon, I frequently observed other heavenly bodies, both fixed stars and planets, with incredible delight; and, when I saw their very great number, I began to consider about a method by which I might be able to measure their distances apart, and at length I found one …

  Now let me review the observations made by me during the two months just past, again inviting the attention of all who are eager for true philosophy to the beginnings which led to the sight of most important phenomena.

  Let me speak first of the surface of the Moon, which is turned towards us. For the sake of being understood more easily, I distinguish two parts in it, which I call respectively the brighter and the darker. The brighter part seems to surround and pervade the whole hemisphere; but the darker part, like a sort of cloud, discolours the Moon’s surface and makes it appear covered with spots. Now these spots, as they are somewhat dark and of considerable size, are plain to every one, and every age has seen them, wherefore I shall call them great or ancient spots, to distinguish them from other spots, smaller in size, but so thickly scattered that they sprinkle the whole surface of the Moon, but especially the brighter portion of it. These spots have never been observed by any one before me; and from my observations of them, often repeated, I have been led to that opinion which I have expressed, namely, that I feel sure that the surface of the Moon is not perfectly smooth, free from inequalities and exactly spherical, as a large school of philosophers considers with regard to the Moon and the other heavenly bodies, but that, on the contrary, it is full of inequalities, uneven, full of hollows and protuberances, just like the surface of the Earth itself, which is varied everywhere by lofty mountains and deep valleys.

  The appearances from which we may gather these conclusions are of the following nature: – On the fourth or fifth day after new-moon, when the Moon presents itself to us with bright horns, the boundary which divides the part in shadow from the enlightened part does not extend continuously in an ellipse, as would happen in the case of a perfectly spherical body, but it is marked out by an irregular, uneven, and very wavy line … for several bright excrescences, as they may be called, extend beyond the boundary of light and shadow into the dark part, and on the other hand pieces of shadow encroach upon the light: – nay, even a great quantity of small blackish spots, altogether separated from the dark part, sprinkle everywhere almost the whole space which is at the time flooded with the Sun’s light, with the exception of that part alone which is occupied by the great and ancient spots. I have noticed that the small spots just mentioned have this common characteristic always and in every case, that they have the dark part towards the Sun’s position, and on the side away from the Sun they have brighter boundaries, as if they were crowned with shining summits. Now we have an appearance quite similar on the Earth about sunrise, when we behold the valleys, not yet flooded with light, but the mountains surrounding them on the side opposite to the Sun already ablaze with the splendour of his beams; and just as the shadows in the hollows of the Earth diminish
in size as the Sun rises higher, so also these spots on the Moon lose their blackness as the illuminated part grows larger and larger. Again, not only are the boundaries of light and shadow in the Moon seen to be uneven and sinuous, but – and this produces still greater astonishment – there appear very many bright points within the darkened portion of the Moon, altogether divided and broken off from the illuminated tract, and separated from it by no inconsiderable interval, which, after a little while, gradually increase in size and brightness, and after an hour or two become joined on to the rest of the bright portion, now become somewhat larger; but in the meantime others, one here and another there, shooting up as if growing, are lighted up within the shaded portion, increase in size, and at last are linked on to the same luminous surface, now still more extended … Now, is it not the case on the Earth before sunrise, that while the level plain is still in shadow, the peaks of the most lofty mountains are illuminated by the Sun’s rays? After a little while does not the light spread further, while the middle and larger parts of those mountains are becoming illuminated; and at length, when the Sun has risen, do not the illuminated parts of the plains and hills join together? The grandeur, however, of such prominences and depressions in the Moon seems to surpass both in magnitude and extent the ruggedness of the Earth’s surface, as I shall hereafter show. And here I cannot refrain from mentioning what a remarkable spectacle I observed while the Moon was rapidly approaching her first quarter … A protuberance of the shadow, of great size, indented the illuminated part in the neighbourhood of the lower cusp; and when I had observed this indentation longer, and had seen that it was dark throughout, at length, after about two hours, a bright peak began to arise a little below the middle of the depression; this by degrees increased, and presented a triangular shape, but was as yet quite detached and separated from the illuminated surface. Soon around it three other small points began to shine, until, when the Moon was just about to set, that triangular figure, having now extended and widened, began to be connected with the rest of the illuminated part, and, still girt with the three bright peaks already mentioned, suddenly burst into the indentation of shadow like a vast promontory of light …

  Galileo goes on to describe the greatly increased number of stars visible through his telescope. The number of stars visible to the naked eye could be counted. But his telescope ‘set distinctly before the eyes other stars in myriads which have never been seen before, and which surpass the old, previously known, stars in number more than ten times’. Turning his telescope to the Milky Way, the nature of which had been in dispute for centuries, he was able to establish that it was ‘a mass of innumerable stars planted in clusters’. He then went on to his most amazing discovery.

  I have now finished my brief account of the observations which I have thus far made with regard to the Moon, the Fixed Stars, and the Galaxy. There remains the matter, which seems to me to deserve to be considered the most important in this work, namely, that I should disclose and publish to the world the occasion of discovering and observing four PLANETS, never seen from the very beginning of the world up to our own times, their positions, and the observations made during the last two months about their movements and their changes of magnitude; and I summon all astronomers to apply themselves to examine and determine their periodic times, which it has not been permitted me to achieve up to this day, owing to the restriction of my time. I give them warning however again, so that they may not approach such an inquiry to no purpose, that they will want a very accurate telescope, and such as I have described in the beginning of this account.

  On the 7th day of January in the present year, 1610, in the first hour of the following night, when I was viewing the constellations of the heavens through a telescope, the planet Jupiter presented itself to my view, and as I had prepared for myself a very excellent instrument, I noticed a circumstance which I had never been able to notice before, owing to want of power in my other telescope, namely, that three little stars, small but very bright, were near the planet; and although I believed them to belong to the number of the fixed stars, yet they made me somewhat wonder, because they seemed to be arranged exactly in a straight line, parallel to the ecliptic, and to be brighter than the rest of the stars, equal to them in magnitude. The position of them with reference to one another and to Jupiter was as follows.

  On the east side there were two stars, and a single one towards the west. The star which was furthest towards the east, and the western star, appeared rather larger than the third.

  I scarcely troubled at all about the distance between them and Jupiter, for, as I have already said, at first I believed them to be fixed stars; but when on January 8th, led by some fatality, I turned again to look at the same part of the heavens, I found a very different state of things, for there were three little stars all west of Jupiter, and nearer together than on the previous night, and they were separated from one another by equal intervals.

  At this point, although I had not turned my thoughts at all upon the approximation of the stars to one another, yet my surprise began to be excited, how Jupiter could one day be found to the east of all the aforesaid fixed stars when the day before it had been west of two of them; and forthwith I became afraid lest the planet might have moved differently from the calculation of astronomers, and so had passed those stars by its own proper motion. I therefore waited for the next night with the most intense longing, but I was disappointed of my hope, for the sky was covered with clouds in every direction.

  But on January 10th the stars appeared in the following position with regard to Jupiter; there were two only, and both on the east side of Jupiter, the third, as I thought, being hidden by the planet. They were situated just as before, exactly in the same straight line with Jupiter, and along the Zodiac.

  When I had seen these phenomena, as I knew that corresponding changes of position could not by any means belong to Jupiter, and as, moreover, I perceived that the stars which I saw had been always the same, for there were no others either in front or behind, within a great distance, along the Zodiac, – at length, changing from doubt into surprise, I discovered that the interchange of position which I saw belonged not to Jupiter, but to the stars to which my attention had been drawn, and I thought therefore that they ought to be observed henceforward with more attention and precision.

  Accordingly, on January 11th I saw an arrangement of the following kind, namely, only two stars to the east of Jupiter, the nearer of which was distant from Jupiter three times as far as from the star further to the east; and the star furthest to the east was nearly twice as large as the other one; whereas on the previous night they had appeared nearly of equal magnitude. I therefore concluded, and decided unhesitatingly, that there are three stars in the heavens moving about Jupiter, as Venus and Mercury round the Sun; which at length was established as clear as daylight by numerous other subsequent observations. These observations also established that there are not only three, but four, erratic sidereal bodies performing their revolutions round Jupiter, observations of whose changes of position made with more exactness on succeeding nights the following account will supply …

  Galileo’s discoveries shattered old beliefs. The mountains and craters on the moon showed that the celestial bodies were not perfect spheres, as had always been thought. The thousands of new stars brought home the littleness of our world, lost in space. Afraid of what he would see, the Professor of Philosophy at Padua refused even to look into Galileo’s telescope. Further, the four new ‘planets’ around Jupiter meant that astrology was false, since it had not taken the influence of these bodies into account. The English diplomat Sir Henry Wotton pointed this out when he wrote from Venice to the Earl of Salisbury on 13 March 1610, enclosing a copy of Galileo’s book.

  Now touching the occurrents of the present, I send herewith unto his Majesty the strangest piece of news (as I may justly call it) that he hath ever yet received from any part of the world; which is the annexed book (come abroad this very day) of the Mathemat
ical Professor at Padua, who by the help of an optical instrument (which both enlargeth and approximated the object) invented first in Flanders, and bettered by himself, hath discovered four new planets rolling about the sphere of Jupiter, besides many other unknown and lastly, that the moon is not spherical but endued with many prominences, and, which is of all the strangest, illuminated with the solar light by reflection from the body of the earth, as he seemeth to say. So as upon the whole subject he hath first overthrown all former astronomy and next all astrology. For the virtue of these new planets must needs vary the judicial part, and why may there not be yet more?

  Galileo became an instant celebrity. He christened the moons of Jupiter ‘the Medicean planets’ after Grand Duke Cosimo II de’ Medici, who became his patron. Invited to Rome in triumph, he was received in audience by Pope Paul V, who refused to let him kneel, and at a grand banquet in his honour his optical instrument was dignified by the Greek name ‘telescope’ – a title conferred by the Marquis of Monticelli.