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XVIII. On certain Dimensional Properties of Matter in the Gaseous State. 
Part I. Experimental Researches on Thermal Transpiration of Gases through Porous 
Plates and on the Laws of Transpiration and Impulsion, including an Experi¬ 
mental Proof that Gas is not a continuous Plenum. 
Part II. On an Extension of the Dynamical Theory of Gas, which includes the Stresses, 
Tangential and Normal, caused by a varying Condition of Gas, and affords an 
Explanation of the Phenomena of Transpiration and Impulsion. 
By Osborne Reynolds, M.A., F.R.S., Professor of Engineering in 
Owens College, Manchester. 
Received January 17,—Read February 6, 1879. 
[Plates 47-49.] 
Table of Contents. 
Part I.—(Experimental). 
Art. Section I. — Introduction. Page. 
1-2. General description of the phenomenon of thermal transpiration.. .. .. . . 729 
3. Correspondence of the results from plates of different coarseness when the densities of 
the gas are inversely as the coarseness of the plates . . .. . . • . • • 730 
4-6. Proof that gas is not a continuous plenum .. . . . . . . . . . . .. 731 
7. The results deduced from the kinetic theory. Impulsion or the phenomena of the 
radiometer .. . . . . .. . . .. .. .. . , .. .. 732 
8. Arrangement of the paper . . .. .. . . .. . . . . . . .. 733 
9. Statement of the laws established by experiment .. . . .. .. . . .. 734 
Section II.—Experiments on thermal transpiration. 
10-16. Description of the apparatus and tests applied ,. . . . . .. . . .. 735 
17-19. Drying the gas. Differences of temperature. The porous plates .. .. .. 739 
20-21. The first results with air. Hydrogen . . . . .. . . . . . . .. 740 
22-23. Maximum difference of pressure. Carbonic acid. Stucco plates . . . . .. 744 
24-27. Corresponding pressures with stucco and meerschaum .. . . . . .. .. 747 
28-30. Logarithmic homologues—a method of reducing the experimental results .. .. 753 
31-32. Comparison of the results with the laws stated in Art. 9 .. .. .. .. .. 758 
Section III.—Experiments on transpiration under pressure. 
33. Graham’s results. Necessity for further experiments .. .. .. .. .. 760 
34-38. The apparatus. Equal volumes. Measurement of the time. Purity of the gases .. 760 
39-40. Experimental results. Comparison of logarithmic homologues . . .. . . .. 763 
41. Relative coarseness of the meerschaum and stucco plates.. .. .. .. .. 767 
MDCCCLXXIX. 5 A 
