## E527 -- Conjectura circa naturam aeris, pro explicandis phaenomenis in atmosphaera observatis.

(A conjecture about the nature of air, by which are to be explained the phenomenon which have been observed in the atmosphere)

Summary:
##### (based on Eric J. Aiton's introduction (written in English) to Opera Omnia Series 2, Volume 31)
In this paper, Euler returns to the problem of the make-up of the atmosphere, fifty years after his paper E7. After describing the general structure of the globules of air (which consist of an outer aqueous crust surrounding a section of the proper matter of air surrounding a core of aether destitute of gravity), he says that the indications from observations of foamy water and soap-bubbles show that the aqueous crust does indeed exist. He also says that when there is fog in the lower atmosphere and clouds above it, vapor has dispersed inside globules of air so that it disturbs the refraction and passage of light rays. Euler also gives two reasons why the proper matter of air travels in circles:
• no other explanation explains elasticity; and
• since heat consists of motion, matter must retain some of its motion in the globules, so that in a confined space, these globules must circulate; furthermore, the fact that there is equal pressure in all directions implies that the motion must be circular.
Euler goes on to assign a speed to every temperature (in particular, he finds the speed of boiling water to be 2150 ft/sec), and the formula that he arrives at agrees with experience since the formula predicts that speed increases as the pressure increases, while the boiling point can be seen to increase as the pressure increases. Further, this formula can be used to determine one of pressure, temperature, density, and humidity given the values of the other three. Euler, however, considered this formula to be especially good at determining the force necessary to compress a given amount of air into a given volume (the most important problem of air measurement). Euler also finds that his formula agrees with Boyle's law for small compressions. Euler also arrives at a formula to determine the altitude from barometer and temperature readings. He also remarks that his hypothesis of how air is made up is useful because of its ability to explain the relationship between pressure and humidity.
###### a.s.
According to the records, it was presented to the St. Petersburg Academy on August 14, 1780.

Publication:
• Originally published in Acta Academiae Scientarum Imperialis Petropolitinae 1779, 1779, pp. 103-161
• Opera Omnia: Series 2, Volume 31, pp. 307 - 328
Documents Available:
• Original Publication: E527