PROPERTIES OP MATTER IN' THE GASEOUS STATE. 
817 
shown by the continuous curvature of the curves which express these results. (See 
Plates 47, 48, and 49.) 
III. The uniformity in direction in which both the time of transpiration under 
pressure (see Tables XIV. to XVII.), and the ratio of the thermal differences of 
pressure to the mean pressure (see Tables III. to XIII.) vary as the density increased. 
IA r . The fact, sufficiently proved by Graham, that, cceteris paribus, the times of 
transpiration are proportional to the ratio of the differences of pressure to the mean 
pressure, the difference of pressure being small. 
V. The fact, to a certain extent taken for granted, that the ratio of the thermal 
differences of pressure to the mean pressure are, cceteris paribus, proportional to the 
ratio of the difference of temperature to the absolute temperature, this ratio being 
small. 
VI. The continual approximation towards constancy of the time of transpiration 
under pressure as the density diminished. (See Tables XIV. to XVII., and diagram 1, 
Plate 47.) 
VII. The relation between the ultimate values of the times of transpiration for 
different gases (air and hydrogen) for small densities ; the times are proportional to the 
square roots of their atomic weights. (See Art. 42.) 
VIII. The fact that the times of transpiration for the same gas in capillary tubes, 
and at considerable densities, are inversely as the density and independent of the 
temperature.— Maxwell* and Graham.! 
IX. The difference in the variation of the times of transpiration for different gases, 
shown by the fact that the logarithmic curves for hydrogen cannot be made to fit those 
for air. (Plates 47, 48, and 49.) 
X. The approximation towards a constant value of the ratio which the thermal 
differences of pressure bear to the mean pressure as the density diminishes, whatever 
be the gas or plate, the ratio is that of the difference of the square roots of the 
absolute temperatures to the square root of the absolute temperature. 
XI. The approximation, as the density increases, to a linear relation between the 
thermal differences of pressure and the reciprocal of the density. 
XII. The difference between the law of variation of the thermal differences of 
pressure for different gases, as shown by the non-agreement of the logarithmic 
homologues for air and hydrogen. (Plates 48 and 49.) 
XIII. The transpiration of a varying mixture of gases through a porous plate. 
—Investigated by Graham. 
104. In order to bring out the agreement of the experimental results with those 
deduced from the equation, we put 
^ for the time of transpiration. 
* Phil. Trans. 1866, pp. 249-268, also note to Art. 94. 
5 M 2 
t Phil. Trans., 1849, pp. 349-362- 
