A conjecture about the nature of air, by which are to be explained the phenomenon which have been observed in the atmosphere
In this work, Euler returns to the problem of the make-up of the atmosphere, fifty years after E7. After describing the general structure of the globules of air (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: (1) no other model explains elasticity; and (2) 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. Euler goes on to assign a "speed" to every temperature (in particular, he finds the speed of boiling water to be 2150 ft/sec). The formula that he arrives at agrees with observation since it 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 also arrives at a formula to determine the altitude from barometer and temperature readings. He remarks that his model for air globules is useful because of its ability to explain the relationship between pressure and humidity. (Based on Eric J. Aiton's introduction to Opera Omnia Series 2, Volume 31.)
Original Source Citation
Acta Academiae Scientiarum Imperialis Petropolitanae, Volume 1779: I, pp. 103-161.
Opera Omnia Citation
Series 2, Volume 31, pp.307-328.