Galileo and Experimentation

Galileo's World at a Glance | Gallery at the Exhibit Website
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How do new instruments extend sensory perception, facilitate new experiments, shape new conceptions, raise new questions and promote quantitative methods?

Galileo’s empirical investigations and innovative scientific instruments opened up new worlds of discovery. His thermoscope facilitated quantitative comparison of temperatures throughout the year and under varying circumstances. When Ferdinand II de Medici founded the Academy of Experiment, or Accademia del Cimento, in Florence, the further investigations of Galileo’s successors using the thermometer, barometer and air pump led to advances in meteorology, physics, chemistry and cosmology.

1. Hero of Alexandria, Spiritalium liber (Urbini, 1575), trans. Federico Commandino, "The Book on Air"
2. Galileo Galilei, Discorso Intorno alle Cose, che Stanno in su l’Acqua (Florence, 1612), 1st ed., "Discourse on Floating Bodies"
3. Arturo Pannochieschi, Considerazioni sopra il Discorso del Sig. Galileo (Pisa, 1612), "Considerations on Galileo's Discourse on Floating Bodies"
4. Galileo (Benedetto Castelli), Risposta alle Opposizioni del S. Lodovico delle Colombe (Florence, 1615), "Response to the Opposition of Lodovico delle Colombe"
5. Galileo Thermoscope replica (Museo Galileo)
6. Accademia del Cimento, Saggi di Naturali Esperienze (Florence, 1666), "Essays on Natural Experiences"
7. Accademia del Cimento, Saggi di Naturali Esperienze (Florence, 1667), "Essays on Natural Experiences"
8. Accademia del Cimento, Saggi di Naturali Esperienze (Naples, 1701), "Essays on Natural Experiences"
9. Blaise Pascal, Traitez de l’Equilibre des Liqueurs (Paris, 1663), "Treatise on the Equilibrium of Fluids"
10. Gaspar Schott, Technica Curiosa (Nuremberg, 1664), "Curious Technology"
11. Otto von Guericke, Experimenta nova (Amsterdam, 1672), "New Experiments"
12. Robert Boyle, New Experiments Physico-Mechanicall, Touching the Spring of the Air (Oxford, 1660)
13. Isaac Newton, Opticks (London, 1704)
14. Gaspard-Gustave de Coriolis, “Sur les Équations du Mouvement Relatif des Systèmes de Corps,” Journal de l’Ecole Royale Polytechnique (Paris, 1835), vol. 15, pp. 144-154., "On the Equations of the Relative Movement of Systems of Bodies"

Innovative scientific instruments, from Galileo’s telescope to his thermoscope, seemed almost like natural magic in the ways they opened up new worlds of discovery. These instruments manifested phenomena never perceived by the senses before, wonders that seemed contrary to common experience.  

Galileo’s thermoscope made it possible to refute a then-widespread belief that well water grows warmer in the winter than in the summer.  Well water does seem warmer in the winter, once our senses grow accustomed to colder temperatures, but the thermoscope demonstrated that it is actually colder in the winter than in the summer.

The barometer revealed how to measure the specific weight of the atmosphere as it presses down upon us. A friend of Galileo’s reported that it was impossible to siphon water over a hill more than 32 feet high. Despite persistent, baffling attempts, it proved impossible to pump water any higher. Galileo’s student Torricelli interpreted this unexpected phenomenon of hydraulics in terms of a balance weighing the atmosphere. The atmosphere pushes down with a pressure that can lift a weight equivalent to a column of water 32 feet high. Galileo suggested that Torricelli use mercury instead of water, which reduced the height of the barometer to less than 800 mm.

At mid-century, Otto Von Guericke demonstrated his air-pump before a crowd of eyewitnesses at Magdeburg by evacuating two 20-inch diameter hemispheres. The pressure of the atmosphere held the hemispheres together so strongly that four pairs of horses in harness together on each side could not pull them apart. This “miracle at Magdeburg,” first reported by Gaspar Schott in 1657, was explained in Guericke’s Experimenta Nova (1672). Experimental use of instruments like the thermometer, barometer and air pump promoted a new way of doing science in which meteorology often led the way.

Further reading:
  • Stillman Drake, Galileo: A Very Short Introduction (Oxford, 2001; originally printed 1983 in the Past Masters series), discussion guide.
  • John Heilbron, Galileo (Oxford, 2010)
  • Matteo Valerian, Galileo: Engineer (Boston Studies in the Philosophy and History of Science, Springer, 2008)
Curators: Kerry Magruder and Brent Purkaple. Links are to the exhibit website, For more information, download the comprehensive, free Exhibit Guide from the iBook Store. Open Educational Resources are available at and ShareOK.