There is one more experiment which I must show, and this will be the last; it is a combination of the last two, and it beautifully shows the difference between an inside and an outside bubble. I have now a plain bubble resting against the side of the pair that I have just been using. The instant that I take out the sealing-wax the two outer bubbles join, while the inner one unharmed and the heavy ring slide down to the bottom of the now single outer bubble (Fig. 66). 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. _Paraffined Sieve._