Fill a glass tumbler with water, throw upon its surface a few fragments or thin shavings of camphor, and they will instantly begin to move, and acquire a motion both progressive and rotary, which will continue for a considerable time. During these rotations if the water be touched by any substance which is at all greasy, the floating particles will quickly dart back, and, as if by a stroke of magic, be instantly deprived of their motion and vivacity.

In like manner, if thin slices of cork be steeped in sulphuric ether in a closed bottle for two or three days, and then placed upon the water, they will rotate for several minutes, like the camphor, until the slices of cork, having discharged all their ether, and become soaked with water, they will keep at rest.

If the water be made hot the motion of the camphor will be more rapid than in cold water, but it will cease in proportionately less time. Thus, provide two glasses, one containing water at fifty-eight degrees, and the other at two hundred and ten degrees; place raspings of camphor upon each at the same time; the camphor in the first glass will rotate for about five hours, until all but a very minute portion has evaporated, while the rotation of the camphor in the hot water will last only nineteen minutes. About half the camphor will pass off and the remaining pieces, instead of being dull, white and opaque, will be vitreous and transparent, and evidently soaked with water. The gyrations, too, which at first will be very rapid, will gradually decline in velocity until they become quite sluggish.

The stilling influence of oil upon waves has become proverbial. The extraordinary manner in which a small quantity of oil instantly spreads over a very large surface of troubled water, and the stealthy manner in which even a rough wind glides over it must have excited the admiration of all who have witnessed it.

By the same principle a drop of oil may be made to stop the motion of the camphor, as follows: Throw some camphor, both in slices and in small particles, upon the surface of water, and while they are rotating dip a glass rod into oil of turpentine. Then allow a single drop thereof to trickle down the inner side of the glass to the surface of the water. The camphor will instantly dart to the opposite point of the liquid surface, and cease to rotate.

If a few drops of sulphuric or muriatic acid be let fall into the water, they will gradually stop the motion of the camphor, but if camphor be dropped into nitric acid, diluted with its own bulk of water, it will rotate rapidly for a few seconds and then stop.

If a piece of the rotating camphor be attentively examined with a lens, the currents of the water can be well distinguished, jetting out, chiefly from the corners of the camphor, and bearing it round with irregular force.

The currents, as given out by the camphor, may also be seen by means of the microscope; a drop or two of pure water being placed upon a slip of glass, with a particle of camphor floating upon it. By this means the current may be detected, and it will be seen that they cause the rotations.

A flat watch-glass may be employed, raised a few inches and supported on a wire ring, kept steady by thrusting one end into an upright piece of wood like a retort stand. Then put the camphor and water in the watch-glass, and place under the frame a sheet of white paper, so that it may receive the shadow of the glass, camphor, etc., to be cast by a steady light, placed above, and somewhat on one side of the watch-glass.

On observing the shadow, which may be considered a magnified representation of the object itself, the rotations and currents can be distinguished.