Can cubit from Galileo Galilei books " Dialogue Concerning the Two Chief World Systems", "Two New Sciences", Newtons "Philosophiae Naturalis Principia Mathematica" or Mikołaj Kopernik books convert to other units like feet, meter, inch or does 1 cubit own different value nowadays?


1 Answer 1


Issues regarding ancient measure systems are not easy to manage...

Galileo Galilei, in Discorsi, uses braccia; the "old" translation by Crew & Di Salvio uses: "cubits".

A braccio in Florence was: 583 mm.

In ancient Rome:

according to Vitruvius, a cubit was equal to $1 \frac 1 2$ Roman feet or 6 palm widths, which is 443.8 mm (17.47 in).

According to Stillman Drake [footnote page 469], the braccio used by Galileo was 21 to 22 inches, i.e. between 533 and 558 mm; he translates it with yard, which is 914 mm (36 in).

In conclusion, we may say that a good approximation for Galilei's braccio is an half-meter.

Regarding Copernicus, the evaluation of ancient astronomers regarding the dimension of planets' orbits was expressed in earth radii, i.e. with a "relative" measure; thus, I think that you can hardly find in his works measures expressed in cubits.

Isaac Newton in the Principia uses (Paris) feet [about 325 mm] and inches; see Book 3, Prop.17, Th.15 for :

And from these measures the circumference of the earth is found to be $123,249,600$ Paris feet, and its semidiameter $19,615,800$ feet, on the hypothesis that the earth is spherical.


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