194 
Proceedings of the Royal Society 
The method employed by Poiseuille in his researches, and which 
is described at length in his Memoir, consisted essentially in 
causing air under a known pressure to force a known quantity of 
the fluid to be experimented upon through tubes of known diameter 
and length, and determining the time employed. 
The following are the general results to which he arrived con- 
cerning the influence of the length and diameter of tubes of smaller 
diameter than a millimetre on the rate of flow of any liquid at a 
constant pressure and temperature : — 
1st. The volumes of liquid flowing in equal times through capil- 
lary tubes of equal length, but of different diameters, are amongst 
themselves as the fourth powers of the diameters. 
2d. The volumes of liquids which flow in equal times through 
capillary tubes of the same diameter, but of different lengths, vary 
inversely as the length of the tubes. 
With regard to the influence of pressure, it was found that the 
rate of flow increased directly as the pressure ; and with regard to 
the temperature, that, as a general rule , the rate of flow of solutions 
increases as the temperature rises. 
With regard to the influence of various substances held in solu- 
tion by a fluid, on the rate of flow, no general law was arrived at, 
connecting it either with chemical constitution, density, capillarity, 
or viscosity.* 
The following are some of the results, extracted from M. Poi- 
seuille’s Memoir — 
I. Tube employed (B) is 64 millimetres long; its diameter is 
0 mm, 249 ; capacity of receiver, 6 0. 0.; pressure, 1 metre; tempera- 
ture, 14°5 C. 
* We may merely allude to the fact that M. Graham succeeded in showing 
a decided connection between the rate of flow of the different hydrates of 
sulphuric acid and their chemical constitution. His very interesting results 
are to be found in a paper' “ On liquid transpiration in relation to chemical 
composition.” ( Philosophical Transactions , 1861, p. 373). 
Time of Flow. 
s. 
1. Distilled water, 
2. Ether, 
3. Alcohol, . 
4. Serum of ox’s blood. 
535-2 
160-0 
1184-5 
1029-0 
