The sidereal messenger of Galileo Galilei : $b and a part of the preface to Kepler's Dioptrics containing the original account of Galileo's astronomical discoveries

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THE SIDEREAL MESSENGER


    RIVINGTONS

    London      _Waterloo Place_

    Oxford      _Magdalen Street_

    Cambridge   _Trinity Street_


[Illustration: GALILEO’S BROKEN LENS.

EXHIBITED IN THE LOAN COLLECTION OF SCIENTIFIC APPARATUS AT THE SOUTH
KENSINGTON MUSEUM, 1876.

_From a photograph of the Science and Art Department, South
Kensington._]




    THE SIDEREAL MESSENGER

    OF

    GALILEO GALILEI

    _AND A PART OF THE PREFACE TO KEPLER’S DIOPTRICS_

    CONTAINING THE ORIGINAL ACCOUNT OF GALILEO’S
    ASTRONOMICAL DISCOVERIES.

    A Translation with Introduction and Notes

    BY

    EDWARD STAFFORD CARLOS, M.A.

    HEAD MATHEMATICAL MASTER IN CHRIST’S HOSPITAL.

    RIVINGTONS
    _WATERLOO PLACE, LONDON_
    Oxford and Cambridge
    MDCCCLXXX




PREFATORY NOTE.


About five years ago I was engaged in preparing a catalogue of the
ancient books which belong to Christ’s Hospital. One portion of these
books consisted of a collection of ancient mathematical works presented
at various times for the use of that part of the school which is known
as the Royal Mathematical Foundation of King Charles II. Amongst
them were some well known by name to every mathematical student, but
which few have ever seen. Perhaps the most interesting of them all
was a little volume, printed in London in 1653, containing Gassendi’s
_Explanation of the Ptolemaic and Copernican Systems of Astronomy_, as
well as that of Tycho Brahe, Galileo’s _Sidereus Nuncius_, and Kepler’s
_Dioptrics_. I found Galileo’s account of his astronomical discoveries
so interesting, both in matter and in style, that I translated it as a
recreation from school-work. I venture to think that others also will
be interested in following Galileo through the apprehension of his
famous discoveries, and in reading the language in which he announced
them.




INTRODUCTION.


In 1609, Galileo, then Professor of Mathematics at Padua, in the
service of the Venetian Republic, heard from a correspondent at Paris
of the invention of a telescope, and set to work to consider how
such an instrument could be made. The result was his invention of
the telescope known by his name, and identical in principle with the
modern opera-glass. In a maritime and warlike State, the advantages
to be expected from such an invention were immediately recognised,
and Galileo was rewarded with a confirmation of his Professorship for
life, and a handsome stipend, in recognition of his invention and
construction of the first telescope seen at Venice. In his pamphlet,
_The Sidereal Messenger_, here translated, Galileo relates how he came
to learn the value of the telescope for astronomical research; and
how his observations were rewarded by numerous discoveries in rapid
succession, and at length by that of Jupiter’s satellites. Galileo at
once saw the value of this discovery as bearing upon the establishment
of the Copernican system of astronomy, which had met with slight
acceptance, and indeed as yet had hardly any recommendation except
that of greater simplicity. Kepler had just published at Prague his
work on the planet Mars (_Commentaria de motibus Stellæ Martis_),
on which he had been engaged apparently for eight years; there he
heard of Galileo’s discoveries, and at length was invited by Galileo
himself, through a common friend, Giuliano de’ Medici, ambassador of
the Grand-Duke of Tuscany, Cosmo de’ Medici II., to the Emperor Rudolph
II., to correspond with Galileo on the subject of these discoveries.
The Emperor also requested his opinion, and Kepler accordingly examined
Galileo’s _Sidereal Messenger_ in a pamphlet, entitled _A Discussion
with the Sidereal Messenger_ (Florence, 1610).

In this _Discussion_ Kepler gives reasons for accepting Galileo’s
observations—although he was not able to verify them from want of
a telescope—and entirely supports Galileo’s views and conclusions,
adducing his own previous speculations, or pointing out, as in the case
of Galileo’s idea of earth-light on the moon, the previous conception
of the same explanation of the phenomenon. He rejects, however,
Galileo’s explanation of the copper colour of the moon in eclipses.
Kepler ends by expressing unbounded enthusiasm at the discovery of
Jupiter’s satellites, and the argument it furnishes in support of the
Copernican theory.

Soon after, in 1611, Kepler published another pamphlet, his
_Narrative_, giving an account of actual observations made in
verification of Galileo’s discoveries by himself and several friends,
whose names he gives, with a telescope made by Galileo, and belonging
to Ernest, Elector and Archbishop of Cologne.