Abstract
The study of astronomy was made possible by the instruments built by the other actors in this intricate and long history: mechanics. In the Hellenistic period, mechanical activity, although scarcely appreciated by philosophers, was most probably practiced by mathematicians. Exemplary is the case of Archimedes, who invented many machines and also offered his studies for military purposes. However, the figure of the mechanic and even mechanics has never enjoyed a good reputation among historians.
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Notes
- 1.
Tr. from Greek by Giuliana Boirivant.
- 2.
From Latin armilla: ring.
- 3.
See Appendix “Positional Astronomy”.
- 4.
Readers interested in learning more about the history and the major builders will find a concise exposition in Darin Hayton’s work (Hayton, 2012).
- 5.
For a description of stereographic projection see the Appendix.
- 6.
Given the index of refraction of the two media n1, n2 and θi, θr the angles to the normal to the separating surfaces of incident and refracted rays holds the ratio \( \frac{\mathit{\sin}{\theta}_i}{\mathit{\sin}{\theta}_r}=\frac{n_2}{n_1} \).
- 7.
The magnifying power of a telescope depends on two parameters: the focal distance F and the brightness f, which are linked through the diameter of the lens D by the relationship: \( f=\frac{F}{D} \) where f, the aperture, is the same dimensional unit found in photographic lenses.
- 8.
- 9.
For a general history of clocks see (Turner, 2022)
- 10.
The Observatory was founded by King Charles II in 1675, after the Great Fire of 1666, and designed by Christopher Wren.
- 11.
See also Eco (2020).
- 12.
The period T varies according to the law: \( T=2\pi \sqrt{\frac{l}{g}} \) where g is the acceleration of gravity and l is the length. In the cycloidal pendulum, the period is given by: \( T=2\pi \sqrt{\frac{4a}{g}} \) where a is the radius of the generating circle of the cycloid.
In practice the pendulum does not correspond to the ideal scheme but consists of a body of mass m made up of the wire and the suspended object. In this case, again for small oscillations, the period of the pendulum is: \( T=2\pi \sqrt{\frac{I}{mgd}} \) where I is the rotational inertia (which depends on length and shape), m the suspended mass and d the distance of the suspension point from the center of mass of the pendulum.
- 13.
The period of a circular oscillator is: \( T=2\pi \sqrt{\frac{I}{mgR}} \) where R is the radius of the balance wheel and I is the rotational inertia.
- 14.
The spiral is not shown; it can be recognized in the left diagram, where the amplitude reduces until a force is applied.
- 15.
A very detailed discussion of the main types of escapements, including design guidelines is Gazeley (1956).
- 16.
The crown wheel has the teeth orthogonal to the wheel plane. It is also called the Catherine wheel because it recalls the shape of the cogwheel depicted in the iconography of St Catherine’s martyrdom.
- 17.
The diagrams of the escapements are taken from Headrick (1997).
- 18.
It consists of an arc spring that presses on an eccentric disc integral with the spring barrel; as the radius with which the spring presses on the disc varies, there is a slowing effect that is greater when the spring is loaded and gradually decreases when the spring is unloaded.
- 19.
The driving spring does not act directly on the gear train, but by means of a very thin chain wound on a cone-shaped barrel with a gradually increasing cross-section. The fusée-and-chain transmission works like an infinitely variable gearbox. It equalises the waning force of the mainspring and makes sure that the movement always receives a constant amount of energy. This keeps the watch running at an exact rate.
- 20.
F = − kE·Δl·x where F is the applied force, kE the elastic constant, Δl the elongation and x its direction.
- 21.
- 22.
The capital of the province of Shen, at the Han time called Kwan-Chung.
- 23.
Ibidem
- 24.
Gear theory will be briefly described in Chap. 15.
- 25.
Coordinated Universal Time.
- 26.
https://www.pensierofilosofico.it/ebooks_file/deinfinitouniverso13588679021.pdf. Accessed September 2022.
- 27.
Tr. by the author.
- 28.
Tr. by the author.
- 29.
The regulator is a high-quality pendulum clock whose sole purpose is to measure time with the utmost precision. It often has dial faces to indicate hours, minutes and seconds and was present in watchmaking workshops before the spread of electronic clocks. Every astronomical observatory had regulators.
- 30.
By examining comet sightings in the years 1456, 1531, 1607, and 1683, he concluded that it was the same comet that was to reoccur in 1758. Prediction fulfilled and the comet was given the name Halley.
- 31.
A reprint has been published by the Antiquarian Horological Society in 2018.
- 32.
From British Museum catalogue.
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Marini, D.L.R. (2023). The Instruments. In: Imago Cosmi. Astronomers' Universe. Springer, Cham. https://doi.org/10.1007/978-3-031-30944-1_6
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