E218  Brief von L. Euler an E Pontoppidan vom 11. Mai 1754
(Letter from Euler to Pontoppidan of May 11, 1754)
Summary:
(based on Eric J. Aiton's introduction (written in English) to Opera Omnia Series 2, Volume 31)
This is Euler's response to six questions that Pontoppidan asked Euler in response to reading
E183; Pontoppidan wanted to write an essay on the newness
of the world and sought Euler's help for some clarification. Euler reiterates his belief that the gradual approach
of the planets toward the sun provides convincing evidence that the system of the world, as we now know it, had
a beginning and will also have an end. He also shows why an aether exists and then goes on to say that Newton's theory of light
is inconsistent with Newton's hypothesis that space is a void. He explains this by saying that if luminous matter does
emanate from the sun with the speed of light that experiment has revealed, then all of space must be filled with this matter.
On the other hand, if, as Euler believes, light is a phenomenon similar to sound, then it must be transmitted through an elastic
fluid that fills up space; such a fluid, however, resists the motions of the planets, and the approach of the planets to the sun
then follows by the laws of mechanics. In answer to Pontoppidan's first question, Euler says that luminous matter tends
to drive the earth away from the sun, but this effect is overwhelmed by the force of gravity. As to Pontoppidan's other
questions, Euler says that they are based on the false assumption that light actually emanates from the sun. Euler concludes
by saying that even though the length of each year has become shorter, so have the days; as a result, the years have continued
to contain the same number of days as before.
a.s.
Publication:

Originally published in Essays sur la nouveaute du monde 171183, 1755, pp.

Opera Omnia: Series 2, Volume 31, pp. 261  264
 Reprinted in E. Pontoppidan, Abhandlung von der Neuigkeit der Welt, Copenhagen 1758, pp.
171183 (with a German translation) [E218a]
 Reprinted in B. Hansted, “Deux pièces peu connues de la correspondance d’Euler”; Bullet. d. sc.
mathem. 32, 1879, pp. 2932 [E218b]
Documents Available:
 Our copy of the original document comes from Hanstead's article (see above), and includes an introduction by Hanstead, Pontoppidan's letter, and Euler's letter: E218
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