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grees."

."* This date is anterior to the ding the first notice which we find of claims both of Santorio and Drebbel, a his having embraced the doctrines of Dutch physician, who was the first to the Copernican astronomy. Most of introduce it into Holland.

our readers are aware of the principles Galileo's thermometer, as we have just of the theory of the celestial motions seen, consisted merely of a glass tube which Copernicus restored; but the num. ending in a bulb, the air in which, being ber of those who possess much knoni partly expelled by heat, was replaced ledge of the cumbrous and unwieldy by water from a glass into which the system which it superseded is perhaps open end of the tube was plunged, and more limited. The present is not a fit the different degrees of temperature opportunity to enter into many details were indicated by the expansion of the respecting it; these will find their proper air which yet remained in the bulb, so place in the History of Astronomy: but that the scale would be the reverse of a brief sketch of its leading principles that of the thermometer now in use, for is necessary to render what follows inthe water would stand at the highest level telligible. in the coldest weather. It was, in truth, The earth was supposed to be ima barometer also, in consequence of the moveably fixed in the centre of the unicommunication between the tube and verse, and immediately surrounding it external air, although Galileo did not the atmospheres of air and fire, beyond intend it for this purpose, and when which the sun, moon, and planets, were he attempted to determine the relative thought to be carried round the earth, weight of the air, employed a contri- fixed each to a separate orb or heaven vance still more imperfect than this rude of solid but transparent matter. The barometer would have been. A passage order of distance in which they were among his posthumous fragments inti- supposed to be placed with regard to mates that he subsequently used spirit the central earth was as follows: The of wine instead of water.

Moon, Mercury, Venus, The Sun, Mars, Viviani attributes an improvement of Jupiter, and Saturn. It became a this imperfect instrument, but without question in the ages immediately prespecifying its nature, to Ferdinand II., ceding Copernicus, whether the Sun a pupil and subsequent patron of Gali was not nearer the Earth than Merleo, and, after the death of his father cury, or at least than Venus; and this Cosmo, reigning duke of Florence. It question was one on which the astrowas still further improved by Ferdi- nomical theorists were then chiefly nand's younger brother, Leopold de divided. Medici, who invented the modern process We possess at this time a curious of expelling all the air from the tube record of a former belief in this arrangeby boiling the spirit of wine in it, and ment of the Sun and planets, in the of hermetically sealing the end of the order in which the days of the week have tube, whilst the contained liquid is in been named from them. According to this expanded state, which deprived it the dreams of Astrology, each planet of its barometrical character, and first was supposed to exert its influence in made it an accurate thermometer. The succession, reckoning from the most final improvement was the employment distant down to the nearest, over each of mercury instead of spirit of wine, hour of the twenty-four. The planet which is recommended by Lana so which was supposed to predominate early as 1670, on account of its equable over the first hour, gave its name to expansion. For further details on the that day.* The general reader will history and use of this instrument, the trace this curious fact more easily with reader may consult the Treatises on the the French or Latin names than with THERMOMETER and PYROMETER. the English, which have been translated

into the titles of the corresponding CHAPTER IV.

Saxon deities. Placing the Sun and Astronomy before Copernicus, Fracas- planets in the following order, and betoro

ginning, for instance, with Monday, Bucon Kepler Galileo's Treatise on the Sphere.

or the Moon's day; Saturn ruled the

second hour of that day, Jupiter the This period of Galileo's lectureship at third, and so round till we come again Padua derives interest from its inclu and again to the Moon on the 8th, 15th,

and 22d hours; Saturn ruled the 23d, Memorie e Lettere di Gal. Galilei, Modena, 1821. † Prodromno all' Arte Maestra. Brescia, 1670.

• Dion Cassius, lib. 37.

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Salurn.

Moon.

Mercury

Jupiler

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Venus.

Mars.

Jupiter the 24th, so that the next day combining different eccentric and epicywould be the day of Mars, or, as the clical motions, so as to represent with Saxons translated it, Tuisco's day, or tolerable fidelity the ever varying pheTuesday. In the same manner the fol nomena of the heavens. Aristotle had lowing days would belong respectively lent his powerful assistance in this, as to Mercury or Woden, Jupiter or Thor, in other branches of natural philosophy, Venus or ea, Saturn or Seater, the in enabling the false system to prevail Sun, and again the Moon. In this man against and obliterate the knowledge of ner the whole week will be found to the true, which, as we gather from his complete the cycle of the seven planets. own writings, was maintained by some

philosophers before his time. Of these ancient opinions, only a few traces now remain, principally preserved in the works of those who were adverse to them. Archimedes says expressly that Aristarchus of Samos, who lived about 300 B. C., taught the immobility of the sun and stars, and that the earth is carried round the central sun.* Aris. totle's words are: “ Most of those who assert that the whole concave is finite, say that the earth is situated in the middle point of the universe: those who are called Pythagoreans, who live

in Italy, are of a contrary opinion. 'uns

For they say that fire is in the centre,

and that the earth, which, according to The other stars were supposed to be

them, is one of the stars, occasions the fixed in an outer orb, beyond which were change of day and night by its own mo. two crystalline spheres, (as they were tion, with which it is carried about the called,) and on the outside of all, the centre." It might be doubtful, upon primum mobile or first moveable, which this passage alone, whether the Pythasphere was supposed to revolve round gorean theory embraced more than the the earth in twenty-four hours, and by

diurnal motion of the earth, but a litits friction, or rather, as most of the phi

tle farther, we find the following passage: losophers of that day chose to term it, by “ Some, as we have said, make the earth the sort of heavenly influence which it to be one of the stars : others say that exercised on the interior orbs, to carry it is placed in the centre of the Universe, them round with a similar motion.

and revolves on a central axis."+ From Hence the diversity of day and night. But beside this principal and general • The pretended translation by Roberval of an motion, each orb was supposed to have

Arabic version of Aristarchus, " De Systemate Mun

di," in which the Copernican system is fully deveone of its own, which was intended to

loped, is spurious. Menage asserts this in his observaaccount for the apparent changes of

tions on Diogen. Laert. lib. 8, sec. 85, tom. ii., p. 389. position of the planets with respect to

(Ed. Amst. 1692.) The commentary contains many

authorities well worth consulting. Delambre, His. the fixed stars and to each uther. This toire de l'Astronomie, infers it from its not containing supposition, however, proving insuf some opinions which Archimedes tells us were held by

Aristarchus. A more direct proof may be gathered ficient to account for all the irregu- from the following blunder of the supposed translator. larities of motion observed, two hy Astronomers had been long aware that the earth potheses were introduced.—First, that from the sun. Roberval wished to claim for Aris

in different parts of her orbit is at different distances to each planet belonged several con tarchus the credit of having known this, and introcentric spheres or heavens, casing each

duced into his book, not only the mention of the fact,

but an explanation of its cause. Accordingly he other like the coats of an onion, and, makes Aristarchus give a reason why the sun's aposecondly, that the centres of these solid gee (or place of greatest distancefrom the earth) must spheres, with which the planet revolved,

always be at the north summer solstice." In fact, it

was there, or nearly so, in Roberval's time, and he were placed in the circumference of a knew not but that it had always been there. It is secondary revolving sphere, the centre however moveable, and, when Aristarchus lived,

was nearly half way between the solstices and equiof which secondary sphere was situated poxes. He therefore would hardly have given a at the earth. They thus acquired the reason for the necessity of a phenomenon of which, if names of Eccentrics or Epicycles, the

he observed anything on the subject, he must have

observed the contrary. The change in the obliquity latter word signifying a circle upon a of the earth's axis to the ecliptie was known in the circle. The whole art of astronomers

time of Roberval, and he accordingly has introduced

the proper value which it had in Aristarchus's time. was then directed towards inventing and † De Coelo. lib. 2.

which, in conjunction with the former castoro, who lived in the sixteenth cenextract, it very plainly appears that the tury, writes in the following terms, in his Pythagoreans maintained both the diur- work entitled Homocentrica, (certainly nal and annual motions of the earth. one of the best productions of the day,)

Some idea of the supererogatory la- in which he endeavours to simplify the bour entailed upon astronomers by the necessary apparatus, and to explain all adoption of the system which places the the phenomena (as the title of his book earth in the centre, may be formed in a implies) by concentric spheres round popular manner by observing, in pass- the earth. " There are some, not only ing through a thickly planted wood, of the ancients but also among the in how complicated a manner the re- moderns, who believe that the stars lative positions of the trees appear at move freely without any such agency ; each step to be continually changing, but it is difficult to conceive in what and by considering the difficulty with manner they have imbued themselves which the laws of their apparent mo

with this notion, since not only reason, tions could be traced, if we were to but the very senses, inform us that all attempt to refer these changes to a real the stars are carried round fastened to motion of the trees instead of the tra- solid spheres." What ideas Fracastoro veller. The apparent complexity in entertained of the evidence of the “senses" the heavens is still greater than in the it is not now easy to guess, but he case suggested ; because, in addition to goes on to give a specimen of the “reathe earth's motions, with which all the soning" which appeared to him so instars appear to be impressed, each of controvertible. “The planets are obthe planets has also a real motion of served to move one while forwards, then its own, which of course greatly con- backwards, now to the right, now to tributes to perpiex and complicate the the left, quicker and slower by turns ; general appearances. Accordingly the which variety is consistent with a comheavens rapidly became, under this sys- pound structure like that of an animal, tem,

which possesses in itself various springs " With centric and eccentric scribbled o'er, and principles of action, but is totally Cycle and epicycle, orb in orb;"#

at variance with our notion of a simple crossing and penetrating each other and undecaying substance like the heain every direction. Maestlin has given vens and heavenly bodies. For that a concise enumeration of the prin- which is simple, is altogether single, cipal orbs which belonged to this and singleness is of one only nature, theory. After warning the readers that and one nature can be the cause of “ they are not mere fictions which only one effect; and therefore it is altohave nothing to correspond with them gether impossible that the stars of themout of the imagination, but that they selves should move with such variety exist really and bodily in the hea- of motion. And besides, if the stars vens,“p he describes seven principal move by themselves, they either move in spheres belonging to each planet, which an empty space, or in a fluid medium he classes as Eccentrics, Epicycles, and like the air. But there cannot be such Concentrepicycles, and explains their a thing as empty space, and if there use in accounting for the planet's re were such a medium, the motion of the volutions, motions of the apogee, and star would occasion condensation and nodes, &c. &c. In what manner this rarefaction in different parts of it, which multitude of solid and crystalline orbs is the property of corruptible bodies were secured from injuring or interfe- and where they exist some violent moring with cach other was not very closely tion is going on; but the heavens are inquired into

incorruptible and are not susceptible The reader will cease to expect any of violent motion, and hence, and from very intelligible explanation of this many other similar reasons, any one and numberless other difficulties which who is not obstinate may satisfy himbelong to this unwieldy machinery self that the stars cannot have any when he is introduced to the reasoning independent motion." by which it was upheld. Gerolamo Fra Some persons may perhaps think that

arguments of this force are unnecessarily Paradise Lost, b. viii. v. 83.

dragged from the obscurity to which + Itaque tam circulos primi motus quam orbes secundorum mobilinm revera in cælesti corpore esse con

they are now for the most part happily cludimus, &c. Non ergo sunt mera tigmenta, quibus consigned; but it is essential, in order extra mentem nihil correspondeat. De Astronomie Hypothesibus disputatio. Heidelberge, their true light, to show how low at this

to set Galileo's character and merits in 1592.

!

M. Maestlini,

now

time philosophy had fallen. For we know to be most false."* Instances of shall form a very inadequate notion of extravagant suppositions and premature his powers and deserts if we do not generalizations are to be found in alcontemplate him in the midst of men most every page of his other great conwho, though of undoubted talent and temporary, Kepler. ingenuity, could so far bewilder them It is with pain that we observe Deselves as to mistake such a string of lambre taking every opportunity, in his unmeaning phrases for argument: we admirable History of Astronomy, to un; must reflect on the difficulty every one

dervalue and sneer at Galileo, seemexperiences in delivering himself from ingly for the sake of elevating the the erroneous impressions of infancy, character of Kepler, who appears his which will remain stamped upon the principal favourite, but whose merit as a imagination in spite of all the efforts of philosopher cannot safely be brought matured reason to erase them, and con into competition with that of his illussider every step of Galileo's course as a trious contemporary. Delambre is estriumph over difficulties of a like nature. pecially dissatisfied with Galileo, for We ought to be fully penetrated with this taking no notice, in his “System of feeling before we sit down to the pe- the World,” of the celebrated laws rusal of his works, every line of which of the planetary motions which Kepwill then increase our admiration of ler discovered, and which are the penetrating acuteness of his inven- inseparably connected with his name. tion and unswerving accuracy of his The analysis of Newton and his sucjudgment. In almost every page we cessors has now identified those apdiscover an allusion to some new ex- parently mysterious laws with the geperiment, or the germ of some new neral phenomena of motion, and has theory; and amid all this wonderful thus entitled them to an attention of fertility it is rarely indeed that we find which, before that time, they were scarcely the exuberance of his imagination worthy ; at any rate not more than is at seducing him from the rigid path of present the empirical law which includes philosophical induction. This is the the distances of all the planets from the more remarkable as he was surrounded sun (roughly taken) in one algebraical by friends and contemporaries of a formula. The observations of Kepler's different temperament and much less day were scarcely accurate enough to cautious disposition. A disadvantageous prove that the relations which he discocontrast is occasionally furnished even vered between the distances of the planets by the sagacious Bacon, who could so far from the sun and the periods of their deviate from the soundprinciples ofinduc- revolutions around him were tive philosophy, as to write, for instance, sarily to be received as demonstrated in the following strain, bordering upon truths; and Galileo surely acted most the worst manner of the Aristotelians : prudently and philosophically in hold

Motion in a circle has no limit, and ing himself altogether aloof from Kepseems to emanate from the appetite of ler's fanciful devices and numeral conthe body, which moves only for the sake cinnities, although, with all the extra of moving, and that it may follow itself vagance, they possessed much of the and seek its own embraces, and put in genius of the Platonic reveries, and al action and enjoy its own nature, and though it did happen that Galileo, by exercise its peculiar operation : on the systematically avoiding them, failed to contrary, motion in a straight line seems recognise some important truths. Gatransitory, and to move towards a limitlileo probably was thinking of those of cessation or rest, and that it may very laws, when he said of Kepler, reach some point, and then put off its “He possesses a bold and free genius, motion."* Bacon rejected all the ma- perhaps too much so; but his mode chinery of the primum mobile and the of philosophizing is widely different from solid spheres, the eccentrics and the mine." We shall have further occasion epicycles, and carried his dislike of in the sequel to recognise the justice of these doctrines so far as to assert this remark. that nothing short of their gross ab In the treatise on the Sphere which surdity could have driven theorists to bears Galileo's name, and which, if he the extravagant supposition of the mo

be indeed the author of it, was composed tion of the earth, which, said he, “ we during the early part of his residence at

• “Nobis constat falsissimum esse.” De Aug. Sci• Opuscula Philosophica, Thema Cæli. ent. lib. 1. c. 3. 1623.

neces

Padua, he also adopts the Ptolemaic although there were not wanting persystem, placing the earth immoveable sons envious of their good understandin the centre, and adducing against its ing, who exerted themselves to provoke motion the usual arguments, which in coolness and quarrel between them. his subsequent writings he ridicules Thus Brutius writes to Kepler in 1602*: and refutes. Some doubts have been “Galileo tells me he has written to yoa, expressed of its authenticity; but, how- and has got your which however ever this may be, we have it under he denied to Magini, and I abused him Galileo's own hand that he taught the for praising you with too many qualifiPtolemaic system, in compliance with cations. I know it to be a fact that, popular prejudices, for some time after both in his lectures, and elsewhere, he he had privately become a convert is publishing your inventions as his to the contrary opinions. In a letter, own; but I have taken care, and shall apparently the first which he wrote to continue to do so, that all this shall Kepler, dated from Padua, 1597, he redound not to his credit but to yours." says, acknowledging the receipt of Kep- The only notice which Kepler took of ler's Mysterium Cosmographicum, “I these repeated insinuations, which aphave as yet read nothing beyond the pear to have been utterly groundless, preface of your book, from which how- was, by renewed expressions of respect ever I catch a glimpse of your meaning, and admiration, to testify the value he and feel great joy on meeting with so set upon his friend and fellow-labourer powerful an associate in the pursuit of in philosophy. truth, and consequently such a friend to truth itself, for it is deplorable that there

CHAPTER V. should be so few who care about truth, Galileo re-elected Professor at Padua and who do not persist in their perverse

- New star-Compass of propormode of philosophizing; but as this is not the fit time for lamenting the me

tion-Capra-Gilbert-Proposals to lancholy condition of our times, but

return to PisaLost writings-Ca

valieri. for congratulating you on your elegant discoveries in confirmation of the truth, Galileo's reputation was now rapidly I shall only add a promise to peruse increasing: his lectures were attended your book dispassionately, and with a by many persons of the highest rank; conviction that I shall find in it much among whom were the Archduke Ferto admire. This I shall do the more dinand, afterwards Emperor of Gerwillingly because many years ago I many, the Landgrave of Hesse, and became a convert to the opinions of the Princes of Alsace and Mantua. On Copernicus,* and by that theory have the expiration of the first period for succeeded in fully explaining many phe- which he had been elected professor, nomena, which on the contrary hypo- he was rechosen for a similar period, thesis are altogether inexplicable. I with a salary increased to 320 Horins. have arranged many arguments and the immediate occasion of this augconfutations of the opposite opinions, mentation is said by Fabronit, to have which however I have not yet dared to arisen out of the malice of an ill wisher publish, fearing the fate of our master of Galileo, who, hoping to do him disCopernicus, who, although he has service, apprized the senate that he was earned immortal fame among a few, not married to Marina Gamba, then yet by an infinite number (for so only living with him, and the mother of his can the number of fools be measured) son Vincenzo. Whether or not the senate is exploded and derided. If there might consider themselves entitled to inwere many such as you, I would ven- quire into the morality of his private ture to publish my speculations; but, life, it was probably from a wish to since that is not so, I shall take time to mark their sense of the informer's imconsider of it.” This interesting letter pert ence, that they returned the brief was the beginning of the friendship of answer, that “if he had a family to these two great men, which lasted un- provide for, he stood the more in need of interruptedly till_1632, the date of an increased stipend." Kepler's death. That extraordinary ge During Galileo's residence at Padua, nius never omitted an opportunity of and, according to Viviani's intimation, testifying his admiration of Galileo, towards the thirtieth year of his age,

that is to say in 1594, he experienced • Id autum ed libentius faciam, quod in Copernici seatentiam multis abhinc annis venerim. - Kepl. • Kepleri Epistolæ. Epistolæ,

† Vitæ Italorum Illustrium,

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