PROPERTIES OF MATTER IN THE GASEOUS STATE. 
757 
still a greater tendency to irregularity than with air, and as this was evidently due 
to diffusion through the india-rubber during the very considerable time (4 or 5 hours) 
winch elapsed before the lower pressures were reached, several independent experi¬ 
ments were made. The diffusiometer being filled with pure hydrogen, was exhausted 
at once down to the particular low pressure at which the reading was taken, so as not 
to allow time for diffusion. 
Differences of temperature brought to light by the log. curves. 
30. The results with stucco plate No. 2 are smaller than with No. 1. At first sight 
it was thought that this difference was entirely owing to No. 2 being somewhat 
coarser than No. 1, but when the logarithmic homologues of the curves for this plate 
came to be compared with those for No. 1 and meerschaum No. 3, after the manner 
described in Art. 28, it became apparent that the difference in the results with plates 
No. 1 and 2 (stucco) was due to two causes. Some of it was due, as had been supposed, 
to the greater coarseness of No. 2, but a large part could only be explained on the 
assumption that from some cause or another the difference of temperature with No. 2 
was less than with No. 1. 
Fig. 7 , 
Log. Pressure. 
In fig. 7 it is seen that in order to bring the log. curves for stucco No. 2 into 
coincidence with the curves for stucco No. 1, it was necessary to increase the abscissae 
of the former by •048— log. IT 17 : while the ordinates had to be increased by T12. 
The difference in the abscissae, as shown in Art. 28, represents the difference due to 
the coarseness of the plate ; thus the openings in No. 2 are IT 17 times as broad as the 
openings in No. 1. And the difference between the differences of the ordinates and the 
abscissae =T12 — -048='064=:log. 1T6 is the logarithm of the effect of a difference of 
temperature, and to produce this effect the temperature of the water would have had 
to be lowered 15°. There was some difference, from 5° to 7°, leaving from 8° to 10° 
to be expressed as due to the bright tin plates and thicker rings. 
