PROFESSOR GRAHAM ON THE MOTION OF GASES. 
357 
Table IV. — Transpiration times of equal volumes, by Capillary K of reduced 
lengths. 
Length of capillary. 
Oxygen. 
Air. 
Hydrogen. 
Carbonic acid. 
4"3125 inches. 
1 
0-8985 
0-4250 
0-7770 
3*25 
1 
0-9035 
0-4176 
0-8059 
2-1875 
1 
0-9121 
0-3969 
0-8446 
1-125 
1 
0-9199 
0-3876 
0-9379 
The absolute times for air, with the tubes of these four different lengths, were 473, 
370, 270 and 178 seconds; the temperature varying from 61° to 63°, and the baro- 
meter from 29‘562 to 29‘782 inches. These times, it will be observed, do not become 
shorter, exactly as the length of the tube is diminished, but less rapidly in a very 
sensible degree. This is owing to the interference of effusion. 
When K was 4*3 125 inches in length it allowed 1 cubic inch of air to pass into a 
vacuum, under the pressure of 1 atmosphere, in 14 seconds; or it discharged 4’3 
cubic inches of air per minute. The discharge by the capillary H of its greatest 
length, 237’875 inches, was 3*84 cubic inches per minute. These two tubes therefore 
offer a nearly equal resistance to the passage of air under pressure. On comparing 
the first lines of Tables II. and IV., however, it will be perceived that the transpira- 
tion rates of hydrogen and carbonic acid are sensibly more normal for the long than 
for the short tube, although the difference is not great. Still it appears that con- 
tracting the diameter of a tube does not produce an equally available resistance as 
increasing its length. In other respects the progress of the deviation from the normal 
transpiration rates of the same gas, and of different gases compared together, in pro- 
portion as the resistance diminishes, appears to follow the same law in the short as 
in the long tube. 
While discussing the properties of capillaries of different dimensions, I may allude 
to results obtained by another capillary M, of the same extreme length, 52’5 inches, 
and of nearly the same resistance as K, but of which the bore was cylindrical and not 
flat like that of K. The bore of M was not highly uniform, 0'75 grain of mercury 
occupying a length of the cavity which varied from 3'3 inches at one end to 2*3 inches 
at the other end of the tube. It was employed with the two-pint aspirator-jar, and 
the fall of the attaclied barometer was observed through the usual range from 28'5 to 
23’5 inches. 
(1.) This capillary gave the transpiration time of air 0'8997, a highly normal 
result. 
(2.) The times for air in two experiments being 1133 and 1132 seconds, the times 
of carbonic acid were 913 and 911 seconds ; thermometer 68° and barometer 29 672. 
Transpiration time of carbonic acid . 07247 
In a second series of experiments made upon the same gases, the times of air being 
1104 and 1103 seconds, the times of carbonic acid were 892 and 892 seconds ; and 
3 A 
MDCCCXLIX. 
