Galileo's telescope - The tube and the housing of the optical parts

Dynamic version

Various materials and techniques for making the tube were experimented by the first telescope makers. The little telescope (fig.1) examined by Giovambattista della Porta (c. 1535-1615) (fig.2) in Naples in the summer of 1609 had, for example, a tube made of tin. To build his first telescope, Galileo (1564-1642) (fig.3) used instead a lead tube, while that of the instrument he presented to the Venetian government (fig.4) was made of tin plate covered in rascia, a fabric made of raw wool that was to be used in Venice to cover gondolas up the end of the 19th century. The only two surviving examples of Galileo's vast production, now in the Institute and Museum of the History of Science in Florence (fig.5), both have wooden tubes: one is made of two hollow half-cylinders covered in paper and held together by four copper wires; the other is made of twenty strips of wood glued onto paper and covered in red leather with gold tooling.

Later the tube became standardised (fig.6). As telescopes grew in size, it became telescopic, that is, made of several sections sliding into one another, to reduce its size when not in use. The preferred material became cardboard (fig.7), lightweight but able to provide the necessary rigidity. The secondary sections (fig.8) were often covered in marbled paper and the main section in finely decorated leather. In the telescopes of English make (fig.9), the eyepiece was usually housed in the tube of largest diameter.

The housing of the optical parts (fig.10) also became more sophisticated. Often fabricated by lathing fine cabinet woods, either domestic like boxwood (fig.11) or exotic like guaiacum (fig.12), they were fitted with screw caps to protect the optical components.

Click on the image to enlarge it


©2008 IMSS · Piazza dei Giudici 1 · 50122 Florence · ITALY