174 Movement of Microscopic Particles [April, 
particles exhibit rather a gentle swaying backwards and 
forwards in no determinate direction ; this motion can be 
well studied in common milk, or in a mixture of oil and 
water thoroughly rubbed together. 
It is natural to enquire how long the pedetic movement 
will go on. Does it exhaust itself rapidly^ ? The experi- 
ments which I have made lead to the opposite conclusion in 
a wonderful degree. Ink which is many months — and pos- 
sibly years — old, and which has been long exposed to the 
air, exhibits the motion in perfection, as already stated. 
Again, by means of a pipette, I took a little of the lees from 
a bottle of port wine which had been lying undisturbed in a 
wine-cellar for several years, and placed a drop under the 
thin glass cover of the microscope plate, with the least 
possible exposure to air. A slow distindt motion of the par- 
ticles was apparent, and it was not increased when some of 
the dregs had been shaken up in a bottle with air. This 
experiment leaves no doubt in my mind that the sediment of 
port wine is in a state of perpetual motion, until it finally 
settles down and attaches itself to the glass. But the most 
surprising fadt elicited in the whole enquiry was furnished 
by two glass tubes containing china clay and distilled water, 
which I corked up in November, 1869, and laid in a drawer 
usually opened several times in the day, so that they would 
be shaken up every now and then ; frequently, too, they 
were shaken up by hand. At long intervals the tubes were 
opened, and drops of the milky liquid examined. Comparing 
the motion of the particles with that of newly-mixed china 
clay and water, no diminution of motion was apparent ; on 
the contrary, the motion seemed to he even more remarkable than 
in a fresh mixture. This observation was confirmed by the 
suspensory power of the liquid. On several occasions, in 
1876 and 1877, I have shaken up the tubes and placed them 
upright in a spot shielded from light. After a lapse of 
eleven days I have found a slight cloud of clay still in 
suspension in the lower part of the water. Thus, after 
a trial of eight or nine years’ duration, we meet with 
the astonishing fadt that the suspensory power and the 
pedetic motion apparently increase with time. In fadt 
this pedetic motion seems to be the best approach yet disco- 
vered to a perpetual motion. The above observations are 
quite in agreement with the statement of Dr. Carpenter 
(“ Microscope,” § 130, p. 169), that the movement has been 
known to continue for many years in a small quantity of 
fluid enclosed between two glasses in an air-tight case. 
Faraday, as we have seen, discarded ordinary eledtricity as 
