GALILEO GALILEI, d. 1642

By PROFESSOR HERBERT DINGLE

HREE hundred years ago this month there died in Arcetri, " blind, old and lonely," a man who gave to Italy and the orld an empire infinitely greater and more lasting than any that e Caesars and Duces have conquered or even dreamed of. To alileo Galilei it was given to enlarge the scope of human know- dge in greater measure than to any man before or since. To more than to any other, we owe the foundations and the rinciples of modern science. From the sorry ruins of Italy's Ise grandeur let us turn for a moment to the real greatness at once was hers.

Galileo was born at Pisa in 1564. He seems, writes Brewster ith unintended irony, " to have been desirous of following the ofession of a painter : but his father had observed decided indi- tons of early genius ; and, though by no means able to afford he resolved to send him to the university to pursue the study medicine." Very soon, however, his innate passion for natural ilosophy asserted itself, and medicine was abandoned for more ndamental studies. The strange views of Copernicus concern- g the motion of the earth opened to his mind a new world, d thenceforth his life was divided between adding by observa- n and reasoning to exact knowledge and confounding his critics the prevailing " Aristotelian " school of philosophy. He was t, as is still sometimes stated, the first inventor of the telescope. hat distinction belongs to an obscure Dutchman, who dis- vered by accident a remarkable property of two lenses. A gue rumour of this occurrence reached Galileo at Venice in whereupon he turned his attention to the subject, dis- vered how the thing could be done, and made a telescope, with stinctive characteristics of his own. What distinguishes alileo from the earlier users of the telescope, however, is not y his deeper understanding of the principles of the instrument, also his immediate perception of its great possibilities. Pre- ously the limit of imagination seems to have been reached in the lisation of its use in battle. Galileo turned it away from the rth towards the sky, and reaped a rich harvest.

The Sidereus Nuncius, or " Sidereal Messenger," a slim volume hich can be read in an hour, contains without doubt more ginal knowledge than any book written before or since. The velations of these first telescopic observations of the heavens, beit with an " optic tube " whose objective was little, if any, ger than a spectacle-lens, included the mountains, valleys and eas" of the Moon, the four great satellites of Jupiter, the escent phase of Venus, spots on the Sun, the stellar character the Milky Way, the richness of stellar clusters, thousands upon ousands of hitherto unknown stars, and indeed a wealth of scovery which cannot be truly represented by any catalogue, wever extended. Small wonder that he turned again and again his instrument with incredibili animi jucunditate.

These discoveries, however, fundamental as they are to the ern view of the universe, do not constitute Galileo's chief im to our admiration and gratitude. Had he not made them, cone else would undoubtedly have done so before long, and en his brilliant interpretations of the phenomena which he saw uld inevitably have come. But how long should we have had Watt for the foundations of physical science to be laid? Galileo s the greatest of the giants on whose shoulders Newton stood

to see still further. His claim to be considered as the founder of modern science is incontestable. Before him there were men— Archimedes, Roger Bacon, Leonardo da Vinci, and others—who had the scientific outlook, but they started no movement and laid down no principles from which knowledge could proceed in un- limited progress. Before Galileo the scientific attitude was that of a crank ; after him it was that of a sage.

It is a pity that Galileo is most widely known for his theological controversies, for these were insignificant compared with ' his fundamental work in science. In the age in which he lived, how- ever, theology and astronomy were not clearly differentiated: the sky was subject-matter for both. The revolutionary character of his discoveries, and the uncompromising manner in which he displayed them, brought him into conflict with the ecclesiastical authorities, and a long dispute culminated in his appearance in his old age before a tribunal of the Inquisition, where, under threat of torture, he abjured his belief in the motion of the earth. The story goes that, on rising from his knees, he exclaimed, " E pur si muove" (" All the same, it does move."), but there is no real evidence for this. The remainder of his life was spent in lenient imprisonment.

There are few more dramatic events in scientific history than Galileo's abjuration, but there is, I think, one in the life of Galileo himself. In 1610 he had observed that Saturn, the most distant planet then known (it is now well situated for observation in the early evening—to the naked eye a single point of baleful light, the only view possible in pre-Galilean days), appeared as a triple body, like three o's, thus—oOo. He announced this in the form of an anagram—a device which he adopted on other occasions also, to refute those of his enemies who accused him of plagiarism. He intended, when they made the discoveries later, then to interpret the anagram and so establish his priority. The solu- tion of the Saturnian anagram was Altissimam planetam ter- geminam observavi (I have observed that the outermost planet is triple).

Concerning this, and indeed all his discoveries, he had other charges to face also. He was a deceiver ; he was deceived himself —what he saw was not in the heavens but in his glass ; the devil was in the telescope, perverting the view ; and so on. All this he countered with argument and ridicule, and went on observing. At the end of 1612 he looked again at Saturn and, behold, it was

single. Picture the scene. Here is this man, confident, even arrogant, in his assurance of superior intellect and knowledge and of the trustworthiness of his instrument, and conscious that in his telescope and his mathematical philosophy he holds, for the first time in history, the key to unimaginable stores of knowledge ; and now, unaccountably, without warning, appears a contradic- tion. He rubs his eyes, examines the telescope, checks the setting and looks again ; and again he sees a single body. It is in-

dubitably Saturn, bin whereas it once appeared triple it now indubitably appears single.

What is to be done? What, indeed, can be done? If he

announces the new discovery he virtually withdraws the earlier one and admits that his enemies were right—the glass has deceived him. If he denies this conclusion he can do so only by dog- matically.denying the evidence of his senses—the very practice

he has scorned in his opponents. If he admits the trustworthiness of the senses, he denies that of reason ; if he acknowledges the authority of reason, he denies the trustworthiness of the senses ; and his whole case rests on the inviolability of both. And, over and above all this, is his own inner perplexity. What actually has happened? Can it really be, after all, that the devil is in his telescope, mocking him? No ; he cannot believe that nature is capricious. But what then, can he believe?

"Looking on Saturn," he writes, " within these few. days, I found it solitary, without the assistance of its accustomed stars, and, in short, perfectly round and defined like Jupiter; and such it still remains. Now, what can be said of so strange a metamorphosis? Are the two smaller stars consumed like the spots on the Sun? Have they suddenly vanished and fled? or has Saturn devoured his own children? Or was the appearance indeed fraud and illusion, with which the glasses have for so long a time mocked me, and so many others who have often observed with me? Now, perhaps, the time is come to revive the withering hopes 01 those who, guided by more profound con- templations, have followed all the fallacies of the new observa- tions, and recognised their impossibilities. I cannot resolve what to say in a chance so strange, so new, and so unexpected; the shortness of the time. he unexampled occurrence, the weakness of my intellect and the terror of being mistaken, have greatly confounded me."

He inclined to the view that the system rotated on an axis and that the three bodies had thus come into the same line of sight. On this hypothesis the missing ones would reappear, as in fact they did. But the details of the appearances did not accord with this explanation, and he died without knowing the truth. Later Huyghens, with better instruments and longer series of observa- tions to guide him, proved that the outer " bodies " were really part of a system of flat rings by which the planet was surrounded, and these were so thin that they disappeared from view when

the earth periodically came into their plane. But Saturn's ring system is unique in the universe as it is known even now : how could Galileo have guessed so strange an explanation? He was no magician, but he possessed a gift more valuable than magic— the ability to pronounce what he called " that wise, ingenious and modest sentence,' I do not know.' "