PROFESSOR GRAHAM ON THE MOTION OF GASES. 
385 
The air was transpired into the two-pint aspirator-jar (capacity about 72 cubic inches) 
upon the plate of the air-pump, for the usual range of the gauge barometer from 28’5 
to 23‘5 inches. Thermometer 66°, external barometer 30' 122 to 30*086 inches. 
Transpiration of equal volumes of Air. 
Density or elasticity. 
Time in seconds. 
Reduced time 
of means. 
Calculated or 
theoretical times. 
Experiment I. 
Experiment II. 
] atmosphere 
1095 
1096 
1095-5 
1095-5 
1*25 atmosphere 
707 
707 
883-1 
884-8 
1'5 atmosphere 
493 
493 
739-3 
737-3 
1‘75 atmosphere 
359 
359 
628-25 
632 
2 atmospheres 
277 
276 
553 
553 
2*25 atmospheres 
218 
217 
489-4 
491-5 
2*5 atmospheres 
176 
176 
440 
442 
The column of “Time in seconds ” contains the times of the fall of the air-pump 
barometer from 28*5 to 23*5 inches actually observed, and which are produced by the 
admission to the aspirator-jar of an equal volume of air of constant density. These 
times must therefore be multiplied by the density in atmospheres of the air transpired, 
to obtain the reduced times of the following column. It will be observed that these 
reduced times are in perfect harmony with the “Calculated times” of the last 
column. Indeed nothing could illustrate more strongly the great precision of which 
transpiration experiments are susceptible, than these results. 
The conclusion to be drawn from the present observations with the capillary M, 
and the old observations with E, as compared with the observations made with the 
short capillary K, is that to bring out the normal effect of densities on transpiration, 
a greater resistance and length of tube are necessary than are required for the ob- 
servations of the normal relations in the transpiration times of such gases as oxygen, 
nitrogen and hydrogen ; for the short capillary K, which fails so much in the law 
of densities, exhibits the other relations nearly with as much accuracy as the long 
capillary M. The marked superiority also of the 20-feet tube E over the 8-inch tube 
K, although the power of resistance of these two capillaries is nearly equal, suggests 
again the idea that resistance produced by elongation of the capillary acts differently 
from an equal resistance produced by contracting the diameter of the capillary, and 
more advantageously in transpiration experiments. 
IV. TRANSPIRATION OF AIR AND OTHER GASES AT DIFFERENT TEMPERATURES. 
The experiments which I have made upon the transpiration of air and also of other 
gases at different temperatures are very numerous, but not altogether satisfactory. 
Looking upon the experiments as only preliminary, I shall confine myself at present 
to a statement of results without detail, and endeavour to return to the subject at 
some future opportunity. 
