2. Liquids are very much less suited than are gases to convincing tests of any kinetic hypothesis, for the reason that prior to Brownian-movement work we had no satisfactory kinetic theory of liquids at all.
3. The absolute amounts of the displacements of a given particle in air are 8 times greater and in hydrogen 15 times greater than in water.
4. By reducing the pressure to low values the displacements can easily be made from 50 to 200 times greater in gases than in liquids.
5. The measurements can be made independently of the most troublesome and uncertain factor involved in Brownian-movement work in liquids, namely, the factor
, which contains the radius of the particle and the law governing its motion through the liquid.
Accordingly, there was begun in the Ryerson Laboratory, in 1910, a series of very careful experiments in Brownian movements in gases. Svedberg,[83] in reviewing this subject in 1913, considers this “the only exact investigation of quantitative Brownian movements in gases.” A brief summary of the method and results was published by the author.[84] A full account was published by Mr. Harvey Fletcher in May, 1911,[85] and further work on the variation of Brownian movements with pressure was presented by the author the year following.[86] The essential contribution of this work as regards method consisted in the two following particulars:
1. By combining the characteristic and fully tested equation of the oil-drop method, namely,
with the Einstein Brownian-movement equation, namely,