_Invention of the telescope—Fracastoro—Porta—Reflecting
telescope—Roger Bacon—Digges—De
Dominis—Jansen—Lipperhey—Galileo constructs
telescopes—Microscopes—Re-elected Professor at Padua for life._
THE year 1609 was signalized by Galileo's discovery of the telescope,
which, in the minds of many, is the principal, if not the sole invention
associated with his name. It cannot be denied that his fame, as the
founder of the school of experimental philosophy, has been in an
unmerited degree cast into the shade by the splendour of his
astronomical discoveries; yet Lagrange[32] surely errs in the opposite
extreme, when he almost denies that these form any real or solid part of
the glory of this great man; and Montucla[33] omits an important
ingredient in his merit, when he (in other respects very justly)
remarks, that it required far less genius to point a telescope towards
the heavens than to trace the unheeded, because daily recurring,
phenomena of motion up to its simple and primary laws. We are to
remember that in the days of Galileo a telescope could scarcely be
pointed to the heavens with impunity, and that a courageous mind was
required to contradict, and a strong one to bear down, a party, who,
when invited to look on any object in the heavens which Aristotle had
never suspected, immediately refused all credit to those senses, to
which, on other occasions, they so confidently appealed. It surely is a
real and solid part of Galileo's glory that he consumed his life in
laborious and indefatigable observations, and that he persevered in
announcing his discoveries undisgusted by the invectives, and undismayed
by the persecutions, to which they subjected him. Plagiarist! liar!
impostor! heretic! were among the expressions of malignant hatred
lavished upon him, and although he also was not without some violent and
foul-mouthed partisans, yet it must be told to his credit that he
himself seldom condescended to notice these torrents of abuse, otherwise
than by good-humoured retorts, and by prosecuting his observations with
renewed assiduity and zeal.
The use of single lenses in aid of the sight had been long known.
Spectacles were in common use at the beginning of the fourteenth
century, and there are several hints, more or less obscure, in many
early writers, of the effects which might be expected from a combination
of glasses; but it does not appear with certainty that any of these
authors had attempted to reduce their ideas to practice. After the
discovery of the telescope, almost every country endeavoured to find in
the writings of its early philosophers traces of the knowledge of such
an instrument, but in general with success very inadequate to the zeal
of their national prepossessions. There are two authors especially to
whom the attention of Kepler and others was turned, immediately upon the
promulgation of the discovery, as containing the germ of it in their
works. These are Baptista Porta, and Gerolamo Fracastoro. We have
already had occasion to quote the Homocentrica of Fracastoro, who died
in 1553; the following expressions, though they seem to refer to actual
experiment, yet fall short of the meaning with which it has been
attempted to invest them. After explaining and commenting on some
phenomena of refraction through different media, to which he was led by
the necessity of reconciling his theory with the variable magnitudes of
the planets, he goes on to say—"For which reason, those things which
are seen at the bottom of water, appear greater than those which are at
the top; and if any one look through two eyeglasses, _one placed upon
the other_, he will see every thing much larger and nearer."[34] It
should seem that this passage (as Delambre has already remarked) rather
refers to the close application of one glass upon another, and it may
fairly be doubted whether anything analogous to the composition of the
telescope was in the writer's thoughts. Baptista Porta writes on the
same subject more fully;—"Concave lenses show distant objects most
clearly, convex those which are nearer, whence they may be used to
assist the sight. With a concave glass distant objects will be seen,
small, but distinct; with a convex one those near at hand, larger, but
confused; _if you know rightly how to combine one of each sort, you
will see both far and near objects larger and clearer_."[35] These words
show, if Porta really was then unacquainted with the telescope, how
close it is possible to pass by an invention without lighting on it, for
of precisely such a combination of a convex and concave lens, fitted to
the ends of an organ pipe by way of tube, did the whole of Galileo's
telescope consist. If Porta had stopped here he might more securely have
enjoyed the reputation of the invention, but he then professes to
describe the construction of his instrument, which has no relation
whatever to his previous remarks. "I shall now endeavour to show in what
manner we may contrive to recognize our friends at the distance of
several miles, and how those of weak sight may read the most minute
letters from a distance. It is an invention of great utility, and
grounded on optical principles, nor is it at all difficult of execution;
but it must be so divulged as not to be understood by the vulgar, and
yet be clear to the sharpsighted." The description which follows seems
far enough removed from the apprehended danger of being too clear, and
indeed every writer who has hitherto quoted it has merely given the
passage in its original Latin, apparently despairing of an intelligible
translation. With some alterations in the punctuation, which appear
necessary to bring it into any grammatical construction,[36] it may be
supposed to bear something like the following meaning:—"Let a view be
contrived in the centre of a mirror, where it is most effective. All the
solar rays are exceedingly dispersed, and do not in the least come
together (in the true centre); but there is a concourse of all the rays
in the central part of the said mirror, half way towards the other
centre, where the cross diameters meet. This view is contrived in the
following manner. A concave cylindrical mirror placed directly in front,
but with its axis inclined, must be adapted to that focus: and let
obtuse angled or right angled triangles be cut out with two cross lines
on each side drawn from the centre, and a glass (_specillum_) will be
completed fit for the purposes we mentioned." If it were not for the
word "_specillum_," which, in the passage immediately preceding this,
Porta[37] contrasts with "_speculum_," and which he afterwards explains
to mean a glass lens, it would be very clear that the foregoing passage
(supposing it to have any meaning) must be referred to a reflecting
telescope, and it is a little singular that while this obscure passage
has attracted universal attention, no one, so far as we are aware, has
taken any notice of the following unequivocal description of the
principal part of Newton's construction of the same instrument. It is in
the 5th chapter of the 17th book, where Porta explains by what device
exceedingly minute letters may be read without difficulty. "Place a
concave mirror so that the back of it may lie against your breast;
opposite to it, and within the burning point, place the writing; put a
plane mirror behind it, that may be under your eyes. Then the images of
the letters which are in the concave mirror, and which the concave has
magnified, will be reflected in the plane mirror, so that you may read
without difficulty."
We have not been able to meet with the Italian translation of Porta's
Natural Magic, which was published in 1611, under his own
superintendence; but the English translator of 1658 would probably have
known if any intelligible interpretation were there given of the
mysterious passage above quoted, and his translation is so devoid of
meaning as strongly to militate against this idea. Porta, indeed,
claimed the invention as his own, and is believed to have hastened his
death, (which happened in 1615, he being then 80 years old,) by the
fatigue of composing a Treatise on the Telescope, in which he had
promised to exhaust the subject. We do not know whether this is the same
work which was published after his death by Stelliola,[38] but which
contains no allusion to Porta's claim, and possibly Stelliola may have
thought it most for his friend's reputation to suppress it. Schott[39]
says, a friend of his had seen Porta's book in manuscript, and that it
did at that time contain the assertion of Porta's title to the
invention. After all it is not improbable that he may have derived his
notions of magnifying distant objects from our celebrated countryman
Roger Bacon, who died about the year 1300. He has been supposed, not
without good grounds, to have been one of the first who recognised the
use of single lenses in producing distinct vision, and he has some
expressions with respect to their combination which promise effects
analogous to those held out by Porta. In "The Admirable Force of Art and
Nature," he says, "Physical figurations are far more strange, for in
such manner may we frame perspects and looking-glasses that one thing
shall appear to be many, as one man shall seeme a whole armie; and
divers sunnes and moones, yea, as many as we please, shall appeare at
one time, &c. And so may the perspects be framed, that things most farre
off may seeme most nigh unto us, and clean contrarie, soe that we may
reade very small letters an incredible distance from us, and behold
things how little soever they be, and make stars to appeare wheresoever
we will, &c. And, besides all these, we may so frame perspects that any
man entering into a house he shall indeed see gold, and silver, and
precious stones, and what else he will, but when he maketh haste to the
place he shall find just nothing." It seems plain, that the author is
here speaking solely of mirrors, and we must not too hastily draw the
conclusion, because in the first and last of these assertions he is, to
a certain extent, borne out by facts, that he therefore was in
possession of a method of accomplishing the middle problem also. In the
previous chapter, he gives a long list of notable things, (much in the
style of the Marquis of Worcester's Century of Inventions) which if we
can really persuade ourselves that he was capable of accomplishing, we
must allow the present age to be still immeasurably inferior to him in
science.
Thomas Digges, in the preface to his Pantometria, (published in 1591)
declares, "My father, by his continuall painfull practises, assisted
with demonstrations mathematicall, was able, and sundry times hath by
proportionall glasses, duely situate in convenient angles, not only
discouered things farre off, read letters, numbered peeces of money,
with the verye coyne and superscription thereof, cast by some of his
freends of purpose, upon downes in open fields; but also, seuen miles
off, declared what hath beene doone at that instant in priuate places.
He hath also sundrie times, by the sunne beames, fired powder and
dischargde ordnance halfe a mile and more distante; which things I am
the boulder to report, for that there are yet living diverse (of these
his dooings) occulati testes, (eye witnesses) and many other matters
farre more strange and rare, which I omit as impertinent to this place."
We find another pretender to the honour of the discovery of the
telescope in the celebrated Antonio de Dominis, Archbishop of Spalatro,
famous in the annals of optics for being one of the first to explain the
theory of the rainbow. Montucla, following P. Boscovich, has scarcely
done justice to De Dominis, whom he treats as a mere pretender and
ignorant person. The indisposition of Boscovich towards him is
sufficiently accounted for by the circumstance of his being a Catholic
prelate who had embraced the cause of Protestantism. His nominal
reconciliation with the Church of Rome would probably not have saved him
from the stake, had not a natural death released him when imprisoned on
that account at Rome. Judgment was pronounced upon him notwithstanding,
and his body and books were publicly burnt in the Campo de Fiori, in
1624. His treatise, De Radiis, (which is very rarely to be met with) was
published by Bartolo after the acknowledged invention of the telescope
by Galileo; but Bartolo tells us, in the preface, that the manuscript
was communicated to him from a collection of papers written 20 years
before, on his inquiring the Archbishop's opinion with respect to the
newly discovered instrument, and that he got leave to publish it, "with
the addition of one or two chapters." The treatise contains a complete
description of a telescope, which, however, is professed merely to be an
improvement on spectacles, and if the author's intention had been to
interpolate an afterwritten account, in order to secure to himself the
undeserved honour of the invention, it seems improbable that he would
have suffered an acknowledgment of additions, previous to publication,
to be inserted in the preface. Besides, the whole tone of the work is
that of a candid and truth-seeking philosopher, very far indeed removed
from being, as Montucla calls him, conspicuous for ignorance even among
the ignorant men of his age. He gives a drawing of a convex and concave
lens, and traces the passage of the rays through them; to which he
subjoins, that he has not satisfied himself with any determination of
the precise distance to which the glasses should be separated, according
to their convexity and concavity, but recommends the proper distance to
be found by actual experiment, and tells us, that the effect of the
instrument will be to prevent the confusion arising from the
interference of the direct and refracted rays, and to magnify the object
by increasing the visible angle under which it is viewed. These, among
the many claimants, are certainly the authors who approached the most
nearly to the discovery: and the reader may judge, from the passages
cited, whether the knowledge of the telescope can with probability be
referred to a period earlier than the commencement of the 17th century.
At all events, we can find no earlier trace of its being applied to any
practical use; the knowledge, if it existed, remained speculative and
barren.
In 1609, Galileo, then being on a visit to a friend at Venice, heard a
rumour of the recent invention, by a Dutch spectacle-maker, of an
instrument which was said to represent distant objects nearer than they
usually appeared. According to his own account, this general rumour,
which was confirmed to him by letters from Paris, was all that he
learned on the subject; and returning to Padua, he immediately applied
himself to consider the means by which such an effect could be produced.
Fuccarius, in an abusive letter which he wrote on the subject, asserts
that one of the Dutch telescopes had been at that time actually brought
to Venice, and that he (Fuccarius) had seen it; which, even if true, is
perfectly consistent with Galileo's statement; and in fact the question,
whether or not Galileo saw the original instrument, becomes important
only from his expressly asserting the contrary, and professing to give
the train of reasoning by which he discovered its principle; so that any
insinuation that he had actually seen the Dutch glass, becomes a direct
impeachment of his veracity. It is certain, from the following extract
of a letter from Lorenzo Pignoria to Paolo Gualdo, that one at least of
the Dutch glasses had been sent to Italy. It is dated Padua, 31st
August, 1609.[40] "We have no news, except the return of His Serene
Highness, and the re-election of the lecturers, among whom Sign. Galileo
has contrived to get 1000 florins for life; and it is said to be on
account of an eyeglass, _like the one which was sent from Flanders to
Cardinal Borghese_. We have seen some here, and truly they succeed
well."
It is allowed by every one that the Dutchman, or rather Zealander, made
his discovery by mere accident, which greatly derogates from any honour
attached to it; but even this diminished degree of credit has been
fiercely disputed. According to one account, which appears consistent
and probable, it had been made for sometime before its importance was in
the slightest degree understood or appreciated, but was set up in the
optician's shop as a curious philosophical toy, showing a large and
inverted image of a weathercock, towards which it was directed. The
Marquis Spinola, chancing to see it, was struck with the phenomenon,
purchased the instrument, and presented it either to the Archduke Albert
of Austria, or to Prince Maurice of Nassau, whose name appears in every
version of the story, and who first entertained the idea of employing it
in military reconnoissances.
Zacharias Jansen, and Henry Lipperhey, two spectacle-makers, living
close to each other, near the church of Middleburg, have both had
strenuous supporters of their title to the invention. A third pretender
appeared afterwards in the person of James Metius of Alkmaer, who is
mentioned by Huyghens and Des Cartes, but his claims rest upon no
authority whatever comparable to that which supports the other two.
About half a century afterwards, Borelli was at the pains to collect and
publish a number of letters and depositions which he procured, as well
on one side as on the other.[41] It seems that the truth lies between
them, and that one, probably Jansen, was the inventor of the
_microscope_, which application of the principle was unquestionably of
an earlier date, perhaps as far back as 1590. Jansen gave one of his
microscopes to the Archduke, who gave it to Cornelius Drebbel, a
salaried mathematician at the court of our James the first, where
William Borelli (not the author above mentioned) saw it many years
afterwards, when ambassador from the United Provinces to England, and
got from Drebbel this account of the quarter whence it came. Lipperhey
afterwards, in 1609, accidentally hit upon the _telescope_, and on the
fame of this discovery it would not be difficult for Jansen, already in
possession of an instrument so much resembling it, to perceive the
slight difference between them, and to construct a telescope
independently of Lipperhey, so that each, with some show of reason,
might claim the priority of the invention. A notion of this kind
reconciles the testimony of many conflicting witnesses on the subject,
some of whom do not seem to distinguish very accurately whether the
telescope or microscope is the instrument to which their evidence
refers. Borelli arrives at the conclusion, that Jansen was the inventor;
but not satisfied with this, he endeavours, with a glaring partiality
which makes his former determination suspicious, to secure for him and
his son the more solid reputation of having anticipated Galileo in the
useful employment of the invention. He has however inserted in his
collections a letter from John the son of Zacharias, in which John,
omitting all mention of his father, speaks of his own observation of the
satellites of Jupiter, evidently seeking to insinuate that they were
earlier than Galileo's; and in this sense the letter has since been
quoted,[42] although it appears from John's own deposition, preserved in
the same collection, that at the time of their discovery he could not
have been more than six years old. An oversight of this sort throws
doubt on the whole of the pretended observations, and indeed the letter
has much the air of being the production of a person imperfectly
informed on the subject on which he writes, and probably was compiled to
suit Borelli's purposes, which were to make Galileo's share in the
invention appear as small as possible.
Galileo himself gives a very intelligible account of the process of
reasoning, by which he detected the secret.—"I argued in the following
manner. The contrivance consists either of one glass or of more—one is
not sufficient, since it must be either convex, concave, or plane; the
last does not produce any sensible alteration in objects, the concave
diminishes them: it is true that the convex magnifies, but it renders
them confused and indistinct; consequently, one glass is insufficient to
produce the desired effect. Proceeding to consider two glasses, and
bearing in mind that the plane glass causes no change, I determined that
the instrument could not consist of the combination of a plane glass
with either of the other two. I therefore applied myself to make
experiments on combinations of the two other kinds, and thus obtained
that of which I was in search." It has been urged against Galileo that,
if he really invented the telescope on theoretical principles, the same
theory ought at once to have conducted him to a more perfect instrument
than that which he at first constructed;[43] but it is plain, from this
statement, that he does not profess to have theorized beyond the
determination of the species of glass which he should employ in his
experiments, and the rest of his operations he avows to have been purely
empirical. Besides, we must take into account the difficulty of grinding
the glasses, particularly when fit tools were yet to be made, and
something must be attributed to Galileo's eagerness to bring his results
to the test of actual experiment, without waiting for that improvement
which a longer delay might and did suggest. Galileo's language bears a
resemblance to the first passage which we quoted from Baptista Porta,
sufficiently close to make it not improbable that he might be assisted
in his inquiries by some recollection of it, and the same passage seems,
in like manner, to have recurred to the mind of Kepler, as soon as he
heard of the invention. Galileo's telescope consisted of a plano-convex
and plano-concave lens, the latter nearest the eye, distant from each
other by the difference of their focal lengths, being, in principle,
exactly the same with the modern opera-glass. He seems to have thought
that the Dutch glass was the same, but this could not be the case, if
the above quoted particular of the _inverted_ weathercock, which belongs
to most traditions of the story, be correct; because it is the
peculiarity of this kind of telescope not to invert objects, and we
should be thus furnished with a demonstrative proof of the falsehood of
Fuccarius's insinuation: in that case the Dutch glass must have been
similar to what was afterwards called the astronomical telescope,
consisting of two convex glasses distant from each other by the sum of
their focal lengths. This supposition is not controverted by the fact,
that this sort of telescope was never employed by astronomers till long
afterwards; for the fame of Galileo's observations, and the superior
excellence of the instruments constructed under his superintendence,
induced every one in the first instance to imitate his constructions as
closely as possible. The astronomical telescope was however eventually
found to possess superior advantages over that which Galileo imagined,
and it is on this latter principle that all modern refracting telescopes
are constructed; the inversion being counteracted in those which are
intended for terrestrial observations, by the introduction of a second
pair of similar glasses, which restore the inverted image to its
original position. For further details on the improvements which have
been subsequently introduced, and on the reflecting telescope, which was
not brought into use till the latter part of the century, the reader is
referred to the Treatise on OPTICAL INSTRUMENTS.
Galileo, about the same time, constructed microscopes on the same
principle, for we find that, in 1612, he presented one to Sigismund,
King of Poland; but his attention being principally devoted to the
employment and perfection of his telescope, the microscope remained a
long time imperfect in his hands: twelve years later, in 1624, he wrote
to P. Federigo Cesi, that he had delayed to send the microscope, the use
of which he there describes, because he had only just brought it to
perfection, having experienced some difficulty in working the glasses.
Schott tells an amusing story, in his "Magic of Nature," of a Bavarian
philosopher, who, travelling in the Tyrol with one of the newly invented
microscopes about him, was taken ill on the road and died. The
authorities of the village took possession of his baggage, and were
proceeding to perform the last duties to his body, when, on examining
the little glass instrument in his pocket, which chanced to contain a
flea, they were struck with the greatest astonishment and terror, and
the poor Bavarian, condemned by acclamation as a sorcerer who was in the
habit of using a portable familiar, was declared unworthy of Christian
burial. Fortunately for his character, some bold sceptic ventured to
open the instrument, and discovered the true nature of the imprisoned
fiend.
As soon as Galileo's first telescope was completed, he returned with it
to Venice, and the extraordinary sensation which it excited tends also
strongly to refute Fuccarius's assertion that the Dutch glass was
already known there. During more than a month Galileo's whole time was
employed in exhibiting his instrument to the principal inhabitants of
Venice, who thronged to his house to satisfy themselves of the truth of
the wonderful stories in circulation; and at the end of that time the
Doge, Leonardo Donati, caused it to be intimated to him that such a
present would not be deemed unacceptable by the senate. Galileo took the
hint, and his complaisance was rewarded by a mandate confirming him for
life in his professorship at Padua, at the same time doubling his yearly
salary, which was thus made to amount to 1000 florins.
It was long before the phrenzy of public curiosity abated. Sirturi
describes a ludicrous violence which was done to himself, when, with the
first telescope which he had succeeded in making, he went up into the
tower of St. Mark, at Venice, in the vain hope of being there entirely
unmolested. Unluckily he was seen by some idlers in the street: a crowd
soon collected round him, who insisted on taking possession of his
instrument, and, handing it one to the other, detained him there for
several hours till their curiosity was satiated, when he was allowed to
return home. Hearing them also inquire eagerly at what inn he lodged, he
thought it better to quit Venice early the next morning, and prosecute
his observations in a less inquisitive neighbourhood.[44] Instruments of
an inferior description were soon manufactured, and vended every where
as philosophical playthings, much in the way in which, in our own time,
the kaleidoscope spread over Europe as fast as travellers could carry
them. But the fabrication of a better sort was long confined, almost
solely, to Galileo and those whom he immediately instructed; and so late
as the year 1637, we find Gaertner, or as he chose to call himself,
Hortensius, assuring Galileo that none could be met with in Holland
sufficiently good to show Jupiter's disc well defined; and in 1634
Gassendi begs for a telescope from Galileo, informing him that he was
unable to procure a good one either in Venice, Paris, or Amsterdam.
The instrument, on its first invention, was generally known by the names
of Galileo's tube, the perspective, the double eye-glass: the names of
telescope and microscope were suggested by Demisiano, as we are told by
Lagalla in his treatise on the Moon.[45]
FOOTNOTES:
[32] Mecanique Analytique.
[33] Histoire des Mathématiques, tom. ii.
[34] "Per duo specilla ocularia si quis perspiciat, altero alteri
superposito, majora multo et propinquiora videbit omnia."—Fracast.
Homocentrica, § 2, c. 8.
[35] Si utrumque recte componere noveris, et longinqua et proxima majora
et clara videbis.—Mag. Nat. lib. 17.
[36] The passage in the original, which is printed alike in the editions
of 1598, 1607, 1619, and 1650, is as follows: Visus constituatur centro
valentissimus speculi, ubi fiet, et valentissimè universales solares
radii disperguntur, et coeunt minimè, sed centro prædicti speculi in
illius medio, ubi diametri transversales, omnium ibi concursus.
Constituitur hoc modo speculum concavum columnare æquidistantibus
lateribus, sed lateri uno obliquo sectionibus illis accomodetur,
trianguli vero obtusianguli, vel orthogonii secentur, hinc inde duobus
transversalibus lineis, ex-centro eductis. Et confectum erit specillum,
ad id, quod diximus utile.
[37] Diximus de Ptolemæi _speculo_, sive _specillo_ potius, quo per
sexcentena millia pervenientes naves conspiciebat.
[38] Il Telescopio, 1627.
[39] Magia Naturæ et Artis Herbipoli, 1657.
[40] Lettère d'Uomini illustri. Venezia, 1744.
[41] Borelli. De vero Telescopii inventore, 1655.
[42] Encyclopædia Britannica. Art. TELESCOPE.
[43] Ibid.
[44] Telescopium, Venetiis, 1619.
[45] De phænomenis in orbe Lunæ. Venetiis, 1612.