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any of those comforts, of which, however, I feel the
want of less than many others ; and, therefore, I say
nothing more on the subject. Finally, on the title and
profession of my service, I should wish that, to the
title of mathematician, his highness would add that
of philosopher, as I profess to have studied a greater
number of years in philosophy, than months in pure
mathematics ; and how I have profited by it, and if
I can or ought to deserve this title, I may let their
highnesses see, as often as it shall please them to give


me an opportunity of discussing such subjects in their
presence with those who are most esteemed in this

During the progress of this negotiation, Galileo went
to Venice., on a visit to a friend,, in the month of April
or May, 1 609. Here he learned, from common rumour,
that a Dutchman, of the name of Jansen, had presented
to prince Maurice of Nassau an optical instrument, which
possessed the singular property of causing distant objects
to appear nearer and larger to the observer. A few days
afterwards, the truth of this report was confirmed by a
letter which he received from James Badovere at Paris,
and he immediately apph'ed himself to the consideration
of the subject. On the first night after his return to
Padua, he found, in the doctrines of refraction, the
principle which he sought. He placed at the ends of a
leaden tube two spectacle glasses, both of which were
plain on one side, while one of them had its other side
convex, and the other its second side concave, and having
applied his eye to the concave glass, he saw objects
pretty large and pretty near him. This little instrument,
which magnified only three times, he carried in triumph
to Venice, where it excited the most intense interest.
Crowds of the principal citizens flocked to his house
to see the magical toy ; and after nearly a month
had been spent in gratifying this epidemical curiosity,
Galileo was led to understand from Leonardo Deodati,
the doge of Venice, that the senate would be highly
gratified by obtaining possession of so extraordinary an
instrument. Galileo instantly complied with the wishes
of his patrons, who acknowledged the present by a man-
date conferring upon him for life his professorship at
Padua, and generously raising his salary from 520 to
1000 florins.

Although we cannot doubt the veracity of Galileo,
when he affirms that he had never seen any of the Dutch
telescopes, yet it is expressly stated by Fuccarius, that
one of these instruments had at this time been brought
to Florence. In a letter from Lorenzo Pignoria to


Paolo Gualdo, dated from Padua, on the 31st of August,
l609, it is expressly said, that, at the re-election of the
professors, Galileo had contrived to obtain 1000 florins
for life, which was alleged to be on account of an eye-
glass like the one which was sent from Flanders to the
Cardinal Borghese.

In a memoir so brief and general as the present, it
would be out of place to discuss the history of this ex-
traordinary invention. AVe have no hesitation in as-
serting that a method of magnifying distant objects was
known to Baptista Porta and others ; but it seems to be
equally certain that an instrument for producing these
effects was first constructed in Holland, and that it was
from that kingdom that Galileo derived the knowledge
of its existence. In considering the contending claims,
which have been urged with all the ardour and partiality
of national feeling, it has been generally overlooked, that
a single convex lens, whose focal length exceeds the
distance at which we examine minute objects, performs
the part of a telescope, when an eye, placed behind it,
sees distinctly the inverted image which it forms. A
lens, twenty feet in focal length, will in this manner
magnify tw r enty times ; and it was by the same principle
that Sir AViDiam Herschel discovered a new satellite
of Saturn, by using only the mirror of his forty-feet
telescope. The instrument presented to prince Maurice,
and which the marquis Spinola found in the Dutch
optician's shop, performing the part of a philosophical
toy, by exhibiting a magnified and inverted image of
a distant weathercock, must have been a single lens such
as we have mentioned, or an astronomical telescope
consisting of two convex lenses. Upon either of these
suppositions, it differed entirely from that which Galileo
constructed ; and the Italian philosopher will be justly
entitled to the honour of having invented that form
of the telescope which still bears his name.

The interest which the exhibition of the telescope
excited at Venice did not soon subside : Serturi describes
it as amounting almost to phrensy. When he himself


had succeeded in making one of these instruments, he
ascended the tower of St. Mark, where he might use it
without molestation. He was recognised, however., by a
crowd in the street ; and such was the eagerness of their
curiosity, that they took possession of the wondrous
tube, and detained the impatient philosopher for several
hours, till they had successively witnessed its effects.
Desirous of obtaining the same gratification for their
friends, they endeavoured to learn the name of the inn
at which he lodged ; but Serturi fortunately overheard
their inquiries, and quitted Venice early next morning,
in order to avoid a second visitation of this new school
of philosophers. The opticians speedily availed them-
selves of this new instrument. Galileo's tube, or the
louble eye-glass, as it was then called, for Demisiano
lad not yet given it the appellation of a telescope, was
nanufactured in great quantities, and in a very superior
nanner. The instruments were purchased merely as
xhilosophical toys, and were carried by travellers into
>very corner of Europe.

The art of grinding and polishing lenses was at this
time very imperfect. Galileo, and those whom he in-
structed, were alone capable of making tolerable instru-
ments. It appears, from the testimony of Gassendi
and Gsertner, that, in 1634, a good telescope could not
be procured in Paris, Venice, or Amsterdam ; and that,
even in l63~, there was not one in Holland which
could show Jupiter's disc well defined.

After Galileo had completed his first instrument,
which magnified only three times, he executed a larger
and more accurate one, with a power of about eight.
(f At length," as he himself remarks, "" sparing nei-
ther labour nor expense," he constructed an instru-
ment so excellent, that it magnified more than thirty

The first celestial object to which Galileo applied his
telescope was the moon, which, to use his own words,
appeared as near as if it had been distant only two
semidiameters of the earth. He then directed it to the


planets and the fixed stars, which he frequently observed
with " incredible satisfaction." *

The observations which he made upon the moon
possessed a high degree of interest. The general re-
semblance of its surface to that of our own globe na-
turally fixed his attention ; and he was soon able to
trace, in almost every part of the lunar disc, ranges of
mountains, deep hollows, and other inequalities, which
reflected from their summits the rays of the rising sun,
while the intervening hollows were still buried in dark-
ness. The dark and luminous spaces he regarded as
indicating seas and continents, which reflected, in dif-
ferent degrees, the incident light of the sun ; and he
ascribed the phosphorescence, as it has been improperly
called, or the secondary light, w r hich is seen on the dark
limb of the moon in her first and last quarters, to
the reflection of the sun's light from the earth.

These discoveries were ill received by the followers
of Aristotle. According to their preconceived opinions,
the moon was perfectly spherical, and perfectly smooth ;
to cover it with mountains, and to scoop it out into
valleys, was an act of impiety which defaced the regular
forms which nature herself had imprinted. It was in
vain that Galileo appealed to the evidence of observation,
and to the actual surface of our own globe. The very
irregularities on the moon were, in his opinion, the
proof of divine wisdom : and had its surface been per-
fectly smooth, it would have been <c but a vast un-
blessed desert, void of animals, of plants, of cities, and
of men ; the abode of silence and inaction ; senseless,
lifeless, soulless, and stripped of all those ornaments
which now render it so various and so beautiful."

In examining the fixed stars, and comparing them
with the planets, Galileo discovered a remarkable dif-
ference in the appearance of their discs. All the planets
appeared with round globular discs like the moon ;
whereas the fixed stars never exhibited any disc at all,
but resembled lucid points sending forth twinkling rays.

* Incredibih animi jucunditate. Sid.


Stars of all magnitudes he found to have the same ap-
pearance ; those of the fifth and sixth magnitude having
the same character when seen through a telescope, as
Sirius, the largest of the stars, when seen by the naked
eye. Upon directing his telescope to nebulge and clus-
ters of stars, he was delighted to find that they consisted
of great numbers of stars which could not be recognised
by unassisted vision. He counted no fewer foxa. forty
in the cluster called the Pleiades, or Seven Stars; and he
has given us drawings of this constellation, as well as of
the belt and sword of Orion, and of the nebula of
Prsesepe. In the great nebula of the Milky Way, he
descried crowds of minute stars ; and he concluded that
this singular portion derived its whiteness from still
smaller stars, which his telescope was unable to separate.
Important and interesting as these discoveries were,
they were thrown into the shade by those to which he
was led during an accurate examination of the planets
with a more powerful telescope. On the 7th of January,
1610, at one o'clock in the morning, when he directed
this telescope to Jupiter, he observed three stars near the
body of the planet; two being to the east and one to
the west of him. They were all in a straight line, and
parallel to the ecliptic, and appeared brighter than other
stars of the same magnitude. Believing them to be fixed
stars, he paid no great attention to their distances from
Jupiter and from one another. On the 8th of January,
however, when, from some cause or other *, he had
been led to observe the stars again, he found a very dif-
ferent arrangement of them : all the three were on the
west side of Jupiter, nearer one another than before, and
almost at equal distances. Though he had not turned
his attention to the extraordinary fact of the mutual
approach of the stars, yet he began to consider how
Jupiter could be found to the east of the three stars,
when only the day before he had been to the west of
two of them. The only explanation which he could give
of this fact was_, that the motion of Jupiter was direct

* Nescio quo fato ductus.


contrary to astronomical calculations; and that he had
got before these two stars by his own motion.

In this dilemma between the testimony of his senses
and the results of calculation,, he waited for the follow-
ing night with the utmost anxiety : but his hopes were
disappointed ; for the heavens were wholly veiled in
clouds. On the tenth., two only of the stars appeared,
and both on the east of the planet. As it was obviously
impossible that Jupiter could have advanced from west
to east on the 8th of January,, and from east to west on
the 10th, Galileo was forced to conclude that the phe-
nomenon which he had observed, arose from the motion
of the stars, and he set himself to observe diligently their
change of place. On the llth, there were still only two
stars ; and both to the east of Jupiter ; but the more
eastern star was now twice as large as the other one,
though on the preceding night they had been perfectly
equal. This fact threw a new light upon Galileo's dif-
ficulties, and he immediately drew the conclusion, which
he considered to be indubitable " that there were in
the heavens three stars which revolved round Jupiter,
in the same manner as Venus and Mercury revolve
round the sun." On the 12th of January, he again ob-
served them in new positions, and of different magni-
tudes ; and, on the 13th, he discovered a fourth star,
which completed the four secondary planets with which
Jupiter is surrounded.

Galileo continued his observations on these bodies
every clear night till the 22d of March, and studied
their motions in reference to fixed stars that were at the
same time within the field of his telescope. Having
thus clearly established that the four new stars were
satellites or moons, which revolved round Jupiter
in the same manner as the moon revolves round our
own globe, he drew up an account of his discovery,
in which he gave to the four new bodies the names of
the Medicean Stars, in honour of his patron, Cosmo de*
Medici, grand duke of Tuscany. This work, under the
title of " Nuncius Sidereus/' or the " Sidereal Messen-


ger," was dedicated to the same prince; and the dedica-
tion bears the date of the 4th of March, only two days
after he concluded his observations.

The importance of this great discovery was instantly
felt by the enemies as well as by the friends of the Co-
pernican system. The planets had hitherto been dis-
tinguished from the fixed stars only by their relative
change of place j but the telescope proved them to be
bodies so near to our own globe as to exhibit well-defined
discs ; while the fixed stars retained, even when magni-
fied, the minuteness of remote and lucid points. The
system of Jupiter, illuminated by four moons performing
their revolutions in different and regular periods, ex-
hibited to our proud reason the comparative insig-
nificance of the globe we inhabit, and proclaimed in
impressive language that that globe was not the centre
of the universe.

The reception which these discoveries met with from
Kepler is highly interesting, and characteristic of the
genius of that great man. He was one day sitting idle,
and thinking of Galileo, when his friend Wachenfels
stopped his carriage at his door, to communicate to him
the intelligence. (C Such a fit of wonder," says he,
" seized me at a report which seemed to be so very
absurd, and I was thrown into such agitation at seeing
an old dispute between us decided in this way, that
between his joy, my colouring, and the laughter of both,
confounded as we were by such a novelty, we were hardly
capable, he of speaking, or I of listening. On our
parting, I immediately began to think how there could
be any addition to the number of the planets, without
overturning my ' Cosmographic Mystery/ according to
which Euclid's five regular solids do not allow more
than six planets round the sun. * * * I am so
far from disbelieving the existence of the four circum-
iovial planets, that I long for a telescope, to anticipate
you, if possible, in discovering two round Mars, as the
proportion seems to require, six or eight round Saturn, and
perhaps one each round Mercury and Venus."


In a very different spirit did the Aristotelians receive
the " Sidereal Messenger " of Galileo. The principal
professor of philosophy at Padua resisted Galileo's re-
peated and urgent entreaties to look at the moon and
planets through his telescope ; and he even laboured to
convince the grand duke that the satellites of Jupiter
could not possibly exist. Sizzi, an astronomer of Flo-
rence,, maintained^ that as there were only seven apertures
in the head two eyes, two ears, two nostrils, and one
mouth and as there were only seven metals, and seven
days in the week, so there could be only seven planets.
He seems, however, to have admitted the visibility
of the four satellites through the telescope j but he
argues, that as they are invisible to the naked eye, they
can exercise no influence on the earth ; and being useless,
they do not therefore exist.

A protege of Kepler's, of the name of Horky, wrote
a volume against Galileo's discovery, after having de-
clared, " that he would never concede his four new
planets to that Italian from Padua, even if he should
die for it." This resolute Aristotelian was at no loss
for arguments. He asserted that he had examined the
heavens through Galileo's own glass, and that no such
thing as a satellite existed round Jupiter. He affirmed,
that he did not more surely know that he had a soul in
his body, than that reflected rays are the sole cause of
Galileo's erroneous observations; and that the only use of
the new planets was to gratify Galileo's thirst for gold,
and afford himself a subject of discussion.

When Horky first presented himself to Kepler, after
the publication of this work, the opinion of his patron
was announced to him by a burst of indignation which
overwhelmed the astonished author. Horky supplicated
mercy for his offence ; and, as Kepler himself informed
Galileo, he took him again into favour, on the condition
that Kepler was to show him Jupiter's satellites ; and
that Horky was not only to see them, but to admit their

When the spirit of philosophy had thus left the in-


dividuals who bore her sacred name, it was fortunate
for science that it found a refuge in the minds of princes.
Notwithstanding the reiterated logic of his philosophical
professor at Padua,, Cosmo de' Medici preferred the tes-
timony of his senses to the syllogisms of his instructor.
He observed the new planets several times, along with
Galileo, at Pisa ; and when he parted with him, he gave
him a present worth more than 1000 florins, and con-
cluded that liberal arrangement to which we have already

As philosopher and principal mathematician to the
grand duke of Tuscany, Galileo now took up his resi-
dence at Florence, with a salary of 1000 florins. No
official duties, excepting that of lecturing occasionally
to sovereign princes, were attached to this appointment;
and it was expressly stipulated that he should enjoy the
most perfect leisure to complets his treatises on the con-
stitution of the universe, on mechanics, and on local
motion. The resignation of his professorship at Padua,
which necessarily followed his new appointment, created
much dissatisfaction in that university : but though
many of his former friends refused at first to hold any
communication with him, this feeling gradually sub-
sided ; and the Venetian senate at last appreciated the
views, as well as the powerful motives, which induced
a stranger to accept of promotion in his native land.

While Galileo was enjoying the reward and the fame
of his great discovery, a new species of enmity was
roused against them. Simon Mayer, an astronomer of
no character, pretended that he had discovered the sa-
tellites of Jupiter before Galileo, and that his first observ-
ation was made on the 29th of December, 1609- Other
astronomers announced the discovery of new satellites :
Scheiner reckoned five, Rheita nine, and others found
even so many as twelve : these satellites, however, were
found to be only fixed stars. The names of Vladisla-
vian, Agrippine, Uranodavian, and Ferdinandotertian,
which were hastily given to these common telescopic
stars, soon disappeared from the page of science, and

c 3


even the splendid telescopes of modern times have not
been able to add another gem to the diadem of Jupiter.

A modern astronomer of no mean celebrity has, even
in the present day, endeavoured to rob Galileo of this
staple article of his reputation. From a careless exa-
mination of the papers of our celebrated countryman,
Thomas Harriot, which baron Zach had made in 1784,
at Petworth, the seat of lord Egremont, this astronomer
has asserted* that Harriot first observed the satellites of
Jupiter on the l6'th of January, l6lO; and continued
his observations till the 25th of February, l6l2. Baron
Zach adds the following extraordinary conclusion :
" Galileo pretends to have discovered them on the 7th of
January, l6'lO; so that it is not improbable that Harriot
was likewise the first discoverer of these attendants of
Jupiter." In a communication which I received from
Dr. Robertson, of Oxford, in 1822t, he informed me
that he had examined a class of Harriot's papers, en-
titled, " De Jovialibus Planetis ; " and that it appears,
from two pages of these papers, that Harriot first ob-
served Jupiter's satellites on the \"th of October, l6lO.
These observations are accompanied with rough drawings
of the positions of the satellites, and rough calculations
of their periodical revolutions. My friend, professor
Rigaud J, who has very recently examined the Harriot
MSS., has confirmed the accuracy of Dr. Robertson's ob-
servations, and has thus restored to Galileo the honour
of being the first and the sole discoverer of these se-
condary planets.

The great success which attended the first telescopic
observations of Galileo, induced him to apply his best
instruments to the other planets of our system. The at-
tempts which had been made to deprive him of the
honour of some of his discoveries, combined, probably,
with a desire to repeat his observations with better tele-
scopes, led him to announce his discoveries under the

* Berlin Ephemeris, 1788.

f Edin. Phil. Journ. vol. vi. p. 313.

i Life and Correspondence of Dr. Bradley. Oxford, 1832, p. 523.


veil of an enigma ; and to invite astronomers to declare,
within a given time, if they had observed any new phe-
nomena in the heavens.

Before the close of l6lO, Galileo excited the cu-
riosity of astronomers, by the publication of his first
enigma. Kepler and others tried in vain to decipher it ;
but in consequence of the emperor Rodolph requesting a
solution of the puzzle, Galileo sent him the following
clue :

" Altissimam planetam tergeminam observavi."
I have observed that the most remote planet is triple.

In explaining more fully the nature of his observation,
Galileo remarked that Saturn was not a single star, but
three together, nearly touching one another : he de-
scribed them as having no relative motion, and as having
the form of three o's, namely, oOo, the central one
being larger than those on each side of it.

Although Galileo had announced that nothing new
appeared in the other planets, yet he soon communicated
to the world another discovery of no slight interest. The
enigmatical letters in which it was concealed, formed
the following sentence :

" Cynthia? figuras eemulatur mater Amorum."
Venus rivals the phases of the moon.

Hitherto, Galileo had observed Venus when her disc
was largely illuminated ; but having directed his tele-
scope to her when she was not far removed from the
sun, he saw her in the form of a crescent, resembling
exactly the moon at the same elongation from the sun.
He continued to observe her night after night, during
the whole time that she could be seen in the course of
her revolution round the sun, and he found that she ex-
hibited the very same phases which resulted from her
motion round that luminary.

Galileo had long contemplated a visit to the metro-
polis of Italy, and he accordingly carried his intentions
into effect in the early part of the year l6ll. Here he
was received with that distinction which was due to his

c 4?


great talents and his extended reputation. Princes,
cardinals., and prelates hastened to do him honour ; and
even those who discredited his discoveries, and dreaded
their results, vied with the true friends of science in
their anxiety to see the first wonder of the age.

In order to show the new celestial phenomena to his
friends at Rome, Galileo took with him his best tele-
scope ; and as he had discovered the spots on the sun's
surface in the month of March, l6l 1, he had the grati-
fication of exhibiting this new wonder to his admiring
disciples. He accordingly erected his telescope in the
Quirinal garden, belonging to cardinal Bandini ; and in
April, Ib'll, he exhibited them to his friends in many
of their most interesting variations. From their change
of position on the sun's disc, Galileo at first inferred,
either that the sun revolved about an axis ; or that other
planets, like Venus and Mercury, revolved so near the
sun as to appear like black spots when they were oppo-
site to his disc. Upon continuing his observations, how-

Online LibraryDionysius LardnerEminent literary and scientific men of Italy, Spain, and Portugal .. (Volume 2) → online text (page 2 of 34)