And now that our time has drawn to a close I must ask you whether that admiration and wonder which we all feel when we play with soap-bubbles has been destroyed by these lectures; or whether now that you know more about them it is not increased. I hope you will all agree with me that the actions upon which such common and every-day phenomena as drops and bubbles depend, actions which have occupied the attention of the greatest philosophers from the time of Newton to the present day, are not so trivial as to be unworthy of the attention of ordinary people like ourselves.
PRACTICAL HINTS.
I hope that the following practical hints may be found useful by those who wish themselves to successfully perform the experiments already described.
Drop with India-rubber Surface.
A sheet of thin india-rubber, about the thickness of that used in air-balls, as it appears before they have been blown out, must be stretched over a ring of wood or metal eighteen inches in diameter, and securely wired round the edge. The wire will hold the india-rubber better if the edge is grooved. This does not succeed if tried on a smaller scale. This experiment was shown by Sir W. Thomson at the Royal Institution.
Jumping Frame.
This is easily made by taking a light glass globe about two inches in diameter, such, for instance, as a silvered ball used to ornament a Christmas-tree or the bulb of a pipette, which is what I used. Pass through the open necks of the bulb a piece of wire about one-twentieth of an inch in diameter, and fix it permanently and water-tight upon the wire by working into the necks melted sealing-wax. An inch or two above the globe, fasten a flat frame of thin wire by soldering, or if this is too difficult, by tying and sealing-wax. A lump of lead must then be fastened or hung on to the lower end, and gradually scraped away until the wire frame will just be unable to force its way through the surface of the water. None of the dimensions or materials mentioned are of importance.