386 Mr. C. Tomlinson on the Motions of Camphor 



few drops of valerianic acid poured into water rise to the surface, 

 go through a variety of contor- 

 tions and evolutions, and ex- 

 cite the astonishment of the 

 observer that dead matter 

 should thus of itself become 

 endowed with such active mo- 

 tion. Some years ago I per- 

 formed this experiment, and 

 had a drawing made of one 

 stage of the contortions. If 

 the annexed figure is sup- 

 posed to be in rapid motion, 

 constantly changing into simi- 

 lar figures, and detaching pear-shaped lenses which immediately 

 become circular, a good idea will be formed of the behaviour 

 of this liquid on the surface of water. A drop of isobutylic 

 alcohol forms a similar figure, only more rapid in its action. 



22. In 1838 I published a new method of producing New- 

 ton's rings 36 . Referring to the facility with which oil spreads 

 over the surface of water, it is stated that any oil, balsam, var- 

 nish, or essence not soluble in water will answer the purpose, or, 

 if the oil or balsam &c. be too viscid, it may be made sufficiently 

 fluid by the action of heat. A single drop of oil &c. may form 

 a circular film from 2 to 5 inches in diameter with or without 

 colour, depending on the thickness. Supposing the film to be 

 without colour, the finger dipped in ether (or a piece of porous 

 wood, or a camePs-hair pencil, or, as was afterwards adopted, 

 a bit of sponge tied over the end of a glass rod) and held over 

 the film, " we instantly see a repulsion or recession of particles ; 

 a black spot is formed ; and round it the seven orders of rings 

 appear in all their lustre and beauty. The rings remain just so 

 long as the finger is wet with ether, which having evaporated, 

 or the wet finger being removed, the rings contract in diameter 

 and disappear altogether. These rings can be formed at any 

 part of the surface of the film, and any number of times while 

 the film endures/' 



Among the conditions enumerated are : — " the glass and the 

 water must be perfectly clean and free from grease; the surface 

 of the water must be perfectly tranquil; a clean glass rod must 

 be dipped into the oil, and a single drop only be placed 



(Torino, 1868), p. 236. Professor Luvini has copied, at pp. 238, 239, the 

 figures of creosote and coriander referred to in notes 23 and 27 . 



36 The Student's Manual of Natural Philosophy, London, 1838. In 

 the chapter entitled " The Soap-bubble," at p. 545. 



