clepsydra

A clepsydra is an ancient timekeeping device that measures time using the flow of water or mercury. The word "clepsydra" comes from the Greek words kleptein ("to steal") and hydōr ("water"). [1, 2, 3]  

How it works [1, 4]  

• Water is poured into a vessel and allowed to flow out through a hole. 

• The level of water remaining in the vessel is measured against graduated lines on the inside. 

• The time is read from the level of water remaining in the vessel. 

History [2]  

• The Egyptians invented the clepsydra to measure time at night. [2]  

• The Greeks called it the "water-clock". [2]  

• The Romans invented a clepsydra that used a float to read the time against a scale on the cylinder wall. [4]  

• Galileo used a mercury clepsydra in the 16th century to time his experiments. [4]  

Uses [4, 5]  

• Clepsydras were used to time speeches. 

• Clepsydras were used to track the days and constellations.

Generative AI is experimental.

[1] https://www.merriam-webster.com/dictionary/clepsydra[2] https://dictionary.cambridge.org/us/dictionary/english/clepsydra[3] https://www.dictionary.com/browse/clepsydra[4] https://www.britannica.com/technology/clepsydra[5] https://www.youtube.com/watch?v=R5slEBS4iRI

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The Theaetetus is one of the narrated dialogues of Plato, and is the only one which is supposed to have been written down. In a short introductory scene, Euclides and Terpsion are described as meeting before the door of Euclides' house in Megara. This may have been a spot familiar to Plato (for Megara was within a walk of Athens), but no importance can be attached to the accidental introduction of the founder of the Megarian philosophy. The real intention of the preface is to create an interest about the person of Theaetetus, who has just been carried up from the army at Corinth in a dying state. The expectation of his death recalls the promise of his youth, and especially the famous conversation which Socrates had with him when he was quite young, a few days before his own trial and death, as we are once more reminded at the end of the dialogue. Yet we may observe that Plato has himself forgotten this, when he represents Euclides as from time to time coming to Athens and correcting the copy from Socrates' own mouth. The narrative, having introduced Theaetetus, and having guaranteed the authenticity of the dialogue (compare Symposium, Phaedo, Parmenides), is then dropped. No further use is made of the device. As Plato himself remarks, who in this as in some other minute points is imitated by Cicero (De Amicitia), the interlocutory words are omitted.

Theaetetus, the hero of the battle of Corinth and of the dialogue, is a disciple of Theodorus, the great geometrician, whose science is thus indicated to be the propaedeutic to philosophy.

Hear here

THEAETETUS: Knowledge was said by us to be true opinion; and true opinion is surely unerring, and the results which follow from it are all noble and good.

SOCRATES: He who led the way into the river, Theaetetus, said 'The experiment will show;' and perhaps if we go forward in the search, we may stumble upon the thing which we are looking for; but if we stay where we are, nothing will come to light.

THEAETETUS: Very true; let us go forward and try.

SOCRATES: The trail soon comes to an end, for a whole profession is against us.

THEAETETUS: How is that, and what profession do you mean?

SOCRATES: The profession of the great wise ones who are called orators and lawyers; for these persuade men by their art and make them think whatever they like, but they do not teach them. Do you imagine that there are any teachers in the world so clever as to be able to convince others of the truth about acts of robbery or violence, of which they were not eye-witnesses, while a little water is flowing in the clepsydra?

THEAETETUS: Certainly not, they can only persuade them.

SOCRATES: And would you not say that persuading them is making them have an opinion?

THEAETETUS: To be sure.

SOCRATES: When, therefore, judges are justly persuaded about matters which you can know only by seeing them, and not in any other way, and when thus judging of them from report they attain a true opinion about them, they judge without knowledge, and yet are rightly persuaded, if they have judged well.

THEAETETUS: Certainly.

SOCRATES: And yet, O my friend, if true opinion in law courts and knowledge are the same, the perfect judge could not have judged rightly without knowledge; and therefore I must infer that they are not the same.

THEAETETUS: That is a distinction, Socrates, which I have heard made by some one else, but I had forgotten it. He said that true opinion, combined with reason, was knowledge, but that the opinion which had no reason was out of the sphere of knowledge; and that things of which there is no rational account are not knowable—such was the singular expression which he used—and that things which have a reason or explanation are knowable.

SOCRATES: Excellent; but then, how did he distinguish between things which are and are not 'knowable'? I wish that you would repeat to me what he said, and then I shall know whether you and I have heard the same tale.

THEAETETUS: I do not know whether I can recall it; but if another person would tell me, I think that I could follow him.