Quelltext der Seite History of Astronomy Forbes 1909 06 Galileo and the telescope - Notions of gravity by Horrocks

{{Werk
|Titel=History of Astronomy
|Autor=Forbes-George
|Copyright=Siehe eLib Lizenzen
|Auflage=1
|Erscheinungsjahr=1909
|Sprache=English
|Verlag=
|Typ=Monographie
|Fachgebiete=103 Physik Astronomie,211 Andere Technische Wissenschaften,601 Geschichte Archäologie
|Tags=Wissenschaftsgeschichte, Astronomie, Physik, Raumfahrt, Teleskop
|Originalsprache=English
|Kurzbeschreibung=Geschichte der Astronomie bis 1909.
|Version=1
|Dinge=Teleskop
}}

HISTORY OF ASTRONOMY

:BY
:GEORGE FORBES,
:M.A., F.R.S., M. INST. C. E.,
:(FORMERLY PROFESSOR OF NATURAL PHILOSOPHY, ANDERSON'S COLLEGE, GLASGOW)

:AUTHOR OF &quot;THE TRANSIT OF VENUS,&quot; RENDU'S &quot;THEORY OF THE :GLACIERS OF SAVOY,&quot; ETC., ETC.

:1909
:BOOK II. THE DYNAMICAL PERIOD




==6. GALILEO AND THE TELESCOPE--NOTIONS OF GRAVITY BY HORROCKS, ETC.==


It is now necessary to leave the subject of dynamical astronomy for a
short time in order to give some account of work in a different
direction originated by a contemporary of Kepler's, his senior in fact
by seven years. Galileo Galilei was born at Pisa in 1564. The most
scientific part of his work dealt with terrestrial dynamics; but one
of those fortunate chances which happen only to really great men put
him in the way of originating a new branch of astronomy.

The laws of motion had not been correctly defined.  The only man of
Galileo's time who seems to have worked successfully in the same
direction as himself was that Admirable Crichton of the Italians,
Leonardo da Vinci. Galileo cleared the ground. It had always been
noticed that things tend to come to rest; a ball rolled on the ground,
a boat moved on the water, a shot fired in the air. Galileo realised
that in all of these cases a resisting force acts to stop the motion,
and he was the first to arrive at the not very obvious law that the
motion of a body will never stop, nor vary its speed, nor change its
direction, except by the action of some force.

It is not very obvious that a light body and a heavy one fall at the
same speed (except for the resistance of the air). Galileo proved this
on paper, but to convince the world he had to experiment from the
leaning tower of Pisa.

At an early age he discovered the principle of isochronism of the
pendulum, which, in the hands of Huyghens in the middle of the
seventeenth century, led to the invention of the pendulum clock,
perhaps the most valuable astronomical instrument ever produced.

These and other discoveries in dynamics may seem very obvious now; but
it is often the most every-day matters which have been found to elude
the inquiries of ordinary minds, and it required a high order of
intellect to unravel the truth and discard the stupid maxims scattered
through the works of Aristotle and accepted on his authority. A blind
worship of scientific authorities has often delayed the progress of
human knowledge, just as too much &quot;instruction&quot; of a youth often ruins
his &quot;education.&quot; Grant, in his history of Physical Astronomy, has well
said that &quot;the sagacity and skill which Galileo displays in resolving
the phenomena of motion into their constituent elements, and hence
deriving the original principles involved in them, will ever assure to
him a distinguished place among those who have extended the domains of
science.&quot;

But it was work of a different kind that established Galileo's popular
reputation. In 1609 Galileo heard that a Dutch spectacle-maker had
combined a pair of lenses so as to magnify distant objects. Working on
this hint, he solved the same problem, first on paper and then in
practice. So he came to make one of the first telescopes ever used in
astronomy. No sooner had he turned it on the heavenly bodies than he
was rewarded by such a shower of startling discoveries as forthwith
made his name the best known in Europe.  He found curious irregular
black spots on the sun, revolving round it in twenty-seven days; hills
and valleys on the moon; the planets showing discs of sensible size,
not points like the fixed stars; Venus showing phases according to her
position in relation to the sun; Jupiter accompanied by four moons;
Saturn with appendages that he could not explain, but unlike the other
planets; the Milky Way composed of a multitude of separate stars.

His fame flew over Europe like magic, and his discoveries were much
discussed--and there were many who refused to believe. Cosmo de Medici
induced him to migrate to Florence to carry on his observations.  He
was received by Paul V., the Pope, at Rome, to whom he explained his
discoveries.

He thought that these discoveries proved the truth of the Copernican
theory of the Earth's motion; and he urged this view on friends and
foes alike.  Although in frequent correspondence with Kepler, he never
alluded to the New Astronomy, and wrote to him extolling the virtue of
epicycles. He loved to argue, never shirked an encounter with any
number of disputants, and laughed as he broke down their arguments.

Through some strange course of events, not easy to follow, the
Copernican theory, whose birth was welcomed by the Church, had now
been taken up by certain anti-clerical agitators, and was opposed by
the cardinals as well as by the dignitaries of the Reformed
Church. Galileo--a good Catholic--got mixed up in these discussions,
although on excellent terms with the Pope and his entourage. At last
it came about that Galileo was summoned to appear at Rome, where he
was charged with holding and teaching heretical opinions about the
movement of the earth; and he then solemnly abjured these
opinions. There has been much exaggeration and misstatement about his
trial and punishment, and for a long time there was a great deal of
bitterness shown on both sides. But the general verdict of the present
day seems to be that, although Galileo himself was treated with
consideration, the hostility of the Church to the views of Copernicus
placed it in opposition also to the true Keplerian system, and this
led to unprofitable controversies.  From the time of Galileo onwards,
for some time, opponents of religion included the theory of the
Earth's motion in their disputations, not so much for the love, or
knowledge, of astronomy, as for the pleasure of putting the Church in
the wrong. This created a great deal of bitterness and intolerance on
both sides. Among the sufferers was Giordano Bruno, a learned
speculative philosopher, who was condemned to be burnt at the stake.

Galileo died on Christmas Day, 1642--the day of Newton's birth. The
further consideration of the grand field of discovery opened out by
Galileo with his telescopes must be now postponed, to avoid
discontinuity in the history of the intellectual development of this
period, which lay in the direction of dynamical, or physical,
astronomy.

Until the time of Kepler no one seems to have conceived the idea of
universal physical forces controlling terrestrial phenomena, and
equally applicable to the heavenly bodies. The grand discovery by
Kepler of the true relationship of the Sun to the Planets, and the
telescopic discoveries of Galileo and of those who followed him,
spread a spirit of inquiry and philosophic thought throughout Europe,
and once more did astronomy rise in estimation; and the irresistible
logic of its mathematical process of reasoning soon placed it in the
position it has ever since occupied as the foremost of the exact
sciences.

The practical application of this process of reasoning was enormously
facilitated by the invention of logarithms by Napier. He was born at
Merchistoun, near Edinburgh, in 1550, and died in 1617. By this system
the tedious arithmetical operations necessary in astronomical
calculations, especially those dealing with the trigonometrical
functions of angles, were so much simplified that Laplace declared
that by this invention the life-work of an astronomer was doubled.

Jeremiah Horrocks (born 1619, died 1641) was an ardent admirer of
Tycho Brahe and Kepler, and was able to improve the Rudolphine tables
so much that he foretold a transit of Venus, in 1639, which these
tables failed to indicate, and was the only observer of it. His life
was short, but he accomplished a great deal, and rightly ascribed the
lunar inequality called _evection_ to variations in the value of
the eccentricity and in the direction of the line of apses, at the
same time correctly assigning _the disturbing force of the Sun_
as the cause. He discovered the errors in Jupiter's calculated place,
due to what we now know as the long inequality of Jupiter and Saturn,
and measured with considerable accuracy the acceleration at that date
of Jupiter's mean motion, and indicated the retardation of Saturn's
mean motion.

Horrocks' investigations, so far as they could be collected, were
published posthumously in 1672, and seldom, if ever, has a man who
lived only twenty-two years originated so much scientific knowledge.

At this period British science received a lasting impetus by the wise
initiation of a much-abused man, Charles II., who founded the Royal
Society of London, and also the Royal Observatory of Greeenwich, where
he established Flamsteed as first Astronomer Royal, especially for
lunar and stellar observations likely to be useful for navigation. At
the same time the French Academy and the Paris Observatory were
founded. All this within fourteen years, 1662-1675.

Meanwhile gravitation in general terms was being discussed by Hooke,
Wren, Halley, and many others.  All of these men felt a repugnance to
accept the idea of a force acting across the empty void of space.
Descartes (1596-1650) proposed an ethereal medium whirling round the
sun with the planets, and having local whirls revolving with the
satellites. As Delambre and Grant have said, this fiction only
retarded the progress of pure science. It had no sort of relation to
the more modern, but equally misleading, &quot;nebular hypothesis.&quot; While
many were talking and guessing, a giant mind was needed at this stage
to make things clear.





*[[History of Astronomy Forbes 1909 07 Newton Law of Universal Gravitation|7. SIR ISAAC NEWTON--LAW OF UNIVERSAL GRAVITATION]]



==Contents==

:[[History_of_Astronomy_Forbes_1909|PREFACE]]

:BOOK I. THE GEOMETRICAL PERIOD

*[[History of Astronomy Forbes 1909 01 Primitive Astronomy and Astrology|1. PRIMITIVE ASTRONOMY AND ASTROLOGY]]

*[[History of Astronomy Forbes 1909 02 Ancient Astronomy - Chinese and Chaldaens|2. ANCIENT ASTRONOMY--CHINESE AND CHALDÆANS]]

*[[History of Astronomy Forbes 1909 03 Ancient Greek Astronomy|3. ANCIENT GREEK ASTRONOMY]]

*[[History of Astronomy Forbes 1909 04 Reign of Epicycles - Ptolemy to Copernicus|4. THE REIGN OF EPICYCLES--FROM PTOLEMY TO COPERNICUS]]


:BOOK II. THE DYNAMICAL PERIOD

*[[History of Astronomy Forbes 1909 05 Discovery of the true solar system - Brahae to Kepler|5. DISCOVERY OF THE TRUE SOLAR SYSTEM--TYCHO BRAHE--KEPLER]]

*[[History of Astronomy Forbes 1909 06 Galileo and the telescope - Notions of gravity by Horrocks|6. GALILEO AND THE TELESCOPE--NOTIONS OF GRAVITY BY HORROCKS, ETC.]]

*[[History of Astronomy Forbes 1909 07 Newton Law of Universal Gravitation|7. SIR ISAAC NEWTON--LAW OF UNIVERSAL GRAVITATION]]

*[[History of Astronomy Forbes 1909 08 Newton successors Halley Euler Lagrange Laplace|8. NEWTON'S SUCCESSORS--HALLEY, EULER, LAGRANGE, LAPLACE, ETC.]]

*[[History of Astronomy Forbes 1909 09 Discovery of new planets Herschel Piazzi Adams Le Verrier|9. DISCOVERY OF NEW PLANETS--HERSCHEL, PIAZZI, ADAMS, AND LE VERRIER]]


:BOOK III. OBSERVATION

*[[History of Astronomy Forbes 1909 10 Instruments of precision - size of the solar system|10. INSTRUMENTS OF PRECISION--SIZE OF THE SOLAR SYSTEM]]

*[[History of Astronomy Forbes 1909 11 History of the telescope spectroscope|11. HISTORY OF THE TELESCOPE--SPECTROSCOPE]]

:BOOK IV. THE PHYSICAL PERIOD

*[[History of Astronomy Forbes 1909 12 The Sun|12. THE SUN]]

*[[History of Astronomy Forbes 1909 13 The Moon and Planets|13. THE MOON AND PLANETS]]

*[[History of Astronomy Forbes 1909 14 Comets and Meteors|14. COMETS AND METEORS]]

*[[History of Astronomy Forbes 1909 15 Stars and Nebulae|15. THE STARS AND NEBULÆ]]

*[[History of Astronomy Forbes 1909 16 Index|INDEX]]





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