366 Mr. Tomlinson s Experiments and [May 



clear musical note by j)assing the moistened finger round the 

 edge of the glass, as has been done in all these experiments. 

 If to dilute nitric acid, sufficient to half fill a large soda 

 water glass, three or four lumps of carbonate of ammonia 

 be added, an active effervescence will of course ensue ; but 

 the same strong, clear note can be produced during the 

 most active effervescence, when small bubbles of carbonic 

 acid rise more than half an inch above the surface of the 

 liquid, and the only difference worthy of remark is, that 

 the moment the finger is removed from the glass the note 

 ceases ; whereas, with the oils and other liquids, whether 

 they vibrate with the glass or do not vibrate at all, the note 

 continues audible for a few seconds after the finger has left 

 the glass. 



38. In the last experiment if the glass be struck it will 

 not, as Chladni says, ring. This striking is, however, at 

 best, but a very imperfect mode of vibrating a glass. It is 

 necessary that every part of the circle should receive an 

 impulse, which it can only do by the moistened finger. If, 

 however, the liberation of carbonic acid be such as to cause 

 bubbles of gas to rise up to the brim, the vibration will 

 certainly be deadened ; as when a saturated solution of 

 carbonate of soda is contained in the glass, if a saturated 

 solution of tartaric acid be added, the liquid will rise up 

 and interrupt the vibration, but if the acid be added in 

 lumps, the note will be uninterrupted. 



39. I now proceed to notice the effects of solids placed 

 on the surface of the vibrating mercury. I placed upon it 

 a small magnetic needle, and as soon as the note was pro- 

 duced by means of the moistened finger, the needle revolved 

 in a contrary direction to the finger, and contrary to the 

 apparent motion of the star, (8.) 



40. I then employed a two inch bar magnet, and this 

 during vibration, assumed a position east and west, as the 

 finger was moved from left to right, and west and east as 

 the motion of the finger was reversed. 



41. I found, however, that unmagnetised iron wire re- 

 volved in an opposite direction to the finger, and as I saw 

 nothing in the experiment (40) to induce me to believe 

 that electricity was induced, I concluded that the efforts 

 of the bar magnet, which was a powerful one, to regain its 



