168 
PROFESSOR 0. REYNOLDS ON THE THEORY OF LUBRICATION 
These times are proportional to 
v 
Where p is the fall of pressure; therefore the times multiplied by the respective falls 
of pressure are proportional to the viscosities. 
The arrangement of apparatus used is shown in fig. 2. 
Fig. 2, 
The test tube (A) containing the fluid to be tested was fixed in a beaker of water, 
which was heated and maintained at any required temperature from below. 
A. syphon (B), made of glass tube -p 6 - inch internal diameter, with the extremity of 
its short limb drawn down to capillary size for a length of about 6 inches, this six 
inches being bent up and down so as only to occupy some 2 inches at the bottom of 
the test tube. The long limb of the syphon extended to about 2 feet below the mean 
level of the fluid in the test tube. Two marks on the test tube at different levels 
served to show when a definite volume had been withdrawn. 
The syphon used was the same for each set of experiments on oil and water, so that 
the pressure urging the fluid through the tube was proportioned to the density of the 
fluids—that is, it was T915 as great for oil as water, disregarding the effect of the 
variation of temperature on volume, which in no case amounted to 1 per cent. 
Experiments were first made with water at different temperatures, the times taken 
for the water to fall from the first mark to the second being carefully noted. The 
syphon was then dried and replaced and oil substituted for water. 
Two sets of similar but entirely different apparatus were used on different occasions, 
different samples of oil being used. In the first set the experiments on oil were made 
