Galileo, illustration of the use of the compass, from Le Operazione del Compasso Geometrico et Militare (The Operation of the Geometric and Military Compass), Padua, 1606

Abstract

Galileo designed his geometric and military compass ("compasso geometrico e militare") in 1597. Known in English as the sector, the compass was widely used until the invention of logarithmic tables. In Galileo's model, an arc could be inserted between the two arms of the compass to make the instrument into a quadrant. A plumb bob could be attached.

ID number

RB-GG1606-2

Title

Kepler - preliminary diagram relating to the orbits of Saturn and Jupiter, from Mysterium cosmographicum

Abstract

With this first diagram, Kepler thought that he had discovered the key to unlocking a geometrical secret about the creation of the universe. His education at the university of Tubingen with Michael Maestlin had already convinced him of the truth of the Copernican system, and starting in 1595, he was trying to explain the relationship among the distances of the planets from the sun and the length of their revolutionaround the sun. The diagram came to Kepler as a revelation. As he was explaining some astrological matters to his students, he drew triangles inscribed in the same circle - or nearly triangles since the end of one made up the beginning of the next one. The crossing points of these triangles formed another circle, half the size of the first one. That proportion, he realized, was the same as the proportion between the orbits of Saturn and Jupiter. The importance of the Mysterium Cosmographicum doesn't lie in its scientific value, but more in Kepler's processes since he didn't just present the result of his researches (such as the world system inscribed in the five regular bodies, which he considered at that time as an real achievement in favor of the Copernican system), but he also shows to the reader all his beginnings and errors, as it is the case with that diagram.

ID number

RB-JK1596-1

Title

Kepler - Table I, Mysterium cosmographicum

ID number

RB-JK1596-2

Title

Kepler - Table II, from Mysterium cosmographicum

ID number

RB-JK1596-3

Title

Kepler - Table IV, from Mysterium cosmographicum

ID number

RB-JK1596-5

Title

Kepler - Table V, from Mysterium cosmographicum

ID number

RB-JK1596-6

Title

Kepler - “Ordo sphaerarum mundi”, from Mysterium cosmographicum

ID number

RB-JK1596-7

Title

Kepler - Title page from De stella nova

ID number

RB-JK1606-1

Title

Kepler - Zodiacal sign, from De stella nova

ID number

RB-JK1606-2

Title

Diagram of eyes, from Astronomia pars optica

ID number

RB-JK1604-1

Title

Kepler - Foldout, from De Cometis

ID number

RB-JK1619B-1

Title

Portrait of Tycho Brahe, from Astronomiae Instauratae Mechanica

Abstract

The engraved portrait by Jacob de Gheyn first appeared as a frontispiece in Tycho's Astronomical Letters of 1596 and was later reprinted. It was done in 1586 when Tycho was 40 years old. He is shown wearing the Danish Order of the Elephant.

ID number

RB-TB1602-1

Title

Small quadrant of gilt brass, from Tycho Brahe, Astronomiae Instauratae Mechanica

ID number

RB-TB1602-2

Title

Medium-sized azimuth quadrant of brass, from Tycho Brahe, Astronomiae Instauratae Mechanica

ID number

RB-TB1602-3

Title

Another azimuth quadrant of brass, from Tycho Brahe, Astronomiae Instauratae Mechanica

ID number

RB-TB1602-4

Title

Astronomical sextant for measuring altitudes, from Tycho Brahe, Astronomiae Instauratae Mechanica

ID number

RB-TB1602-5

Title

Revolving azimuth quadrant, from Tycho Brahe, Astronomiae Instauratae Mechanica

ID number

RB-TB1602-6

Title

Great steel quadrant, inscribed in a square, also of steel, and revolving in azimuth, from Tycho Brahe, Astronomiae Instauratae Mechanica

ID number

RB-TB1602-7

Title

Great azimuth semicircle, from Tycho Brahe, Astronomiae Instauratae Mechanica

ID number

RB-TB1602-8

Title

Zodiacal armillary instrument, from Tycho Brahe, Astronomiae Instauratae Mechanica