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PDX OPERAbeat | A Company Blog is the blog for all things Portland Opera, featuring a variety of guest contributors who will provide insider's tidbits on all we do to celebrate the beauty and breadth of opera.

Galileo Galilei Scene 8: Lamps


scene 8


Okay, so first of all, Scene 8 might be my favorite. (But when I write about Scene 2 I might tell you that one is my favorite. Forgive me. I just don't know, you guys).


In this scene, Galileo and his young daughter sit in church, listening to the priest recite Mass. Maria Celeste (her given name was actually Virginia; she became Maria Celeste when she entered the convent) asks Galileo, "Father, what does the Latin say?" Galileo translates for her. "It says, 'Every word of the Bible is sacred, as though descended from heaven.'" The priest continues to deliver the Mass, and Maria Celeste begins, haltingly, to translate the Latin herself. "The Lord laid down the foundations of the earth, that it not be moved forever."


Meanwhile, Galileo has become distracted. As the Mass goes on, Maria Celeste notices the change in the focus of his attention and asks him what he's looking at. "I am looking at the light," he tells her, and then asks her to look up and tell him what she sees. "It's only the chandelier swinging like a pendulum," she answers. He asks her which takes longer, the pendulum swinging a small distance, or a large one, and when she responds -- that presumably it would take the pendulum farther to cover a long distance -- he gently corrects her. No matter how far the pendulum travels, he says, it takes the same amount of time. "But how can you know?" she asks, and he explains that he uses his pulse to time each swing. He comments on the deep and utter perfection of God's world, and remarks that observation of the world is another way of praising the lord.


scene 8


The Pendulum

It's actually up for debate whether or not Galileo first became interested in pendulums after observing the motions of a cathedral chandelier. (The story originates with his first biographer, Viviani, who was also a pupil of Galileo's and may have made up some of his stories to glorify his mentor). Regardless of what initially piqued his interest, Galileo began conducting formal experiments with pendulums in 1602. Galileo and his students measured the number of oscillations a pendulum passed through in an entire day, so that they could determine the pendulum's precise period (the amount of time a pendulum takes to swing from its start point to its end point and back). Having discovered that the pendulum has a constant period -- that is, that no matter how far you swing it, the time it takes a pendulum to swing from one end of its arc to the other is the same -- he began to use the pendulum to measure short periods of time (including his experiments on the inclined plane, which I'll tell you about in Scene 6).


Pendulums were, in fact, the most accurate timekeeping technology for over 300 years. Isn't that cool?!


He also discovered, just as he tells Maria Celeste in the opera, that it didn't matter if the arc of the pendulum were 2 degrees or 80 degrees; the pendulum took the same amount of time to travel from point to point.

galileo's pendulum


Other things Galileo discovered in his experiments with pendulums:


• Pendulums return nearly to their release heights, but not quite

• All pendulums eventually come to rest, with the lighter ones coming to rest faster.

• The period is independent of the weight: that is, that no matter how heavy a pendulum is, it takes the same amount of time to travel from point to point.


Today we know that, in truth, the period of the pendulum will remain constant so long as the angle is kept at about 20 degrees (and even then, it's not totally precise). A pendulum moving along a larger arc will, counterintuitively, take slightly less time to traverse its full distance, because it falls from a greater height and at a more acute angle, and therefore it travels at a greater speed. The difference in time, however, is so minute that it would not have been detectable in Galileo's day.


If you would like to play with Galileo's pendulum experiments, NOVA has a really wonderful interactive tool, which you can find here.