354 On the Forms and States of Fluids [ 1 83 1 . 



that vibrating motion in directions perpendicular to the force 

 applied (105), by which the water can most readily accommo- 

 date itself to rapid, regular, and alternating changes in bulk in 

 the immediate neighbourhood of the oscillating parts. 



119. From this view of the effect it was evident that similar 

 phenomena would be produced if a substance were made to 

 vibrate in contact with and normally to the surface of a fluid, 

 or indeed in any other direction. A lath was therefore fixed 

 horizontally in a vice by one end, so that the other could vibrate 

 vertically ; a cork was cemented to the under surface of the 

 free end, and a basin of water placed beneath with its surface 

 just touching the cork ; on vi- Y\%. 29. 



brating the lath by means of the 

 glass rod andfingers(6T), a beau- 

 tiful and regular star of ridges 

 two, three, or even four inches 

 in length, was formed round 

 the cork, fig. 29. These ridges 

 were more or less numerous ac- 

 cording to the number of vibrations, &c. As the water was 

 raised, and more of the cylinder immersed, the ridges dimi- 

 ished in strength, and at last disappeared : when the cylinder 

 of cork just touched the surface, they were most powerfully 

 developed. This is a necessary consequence of the dependence 

 of the ridges upon the portion of water which is vertically dis- 

 placed and restored at each vibration. When that, being par- 

 tial in relation to the whole surface, is at or near the surface, 

 the ridges are freely formed in the immediate vicinity ; when 

 at a greater depth (being always at the bottom of the cork), 

 the displacement is diffused over a larger mass and surface, 

 each particle moves through less space and with less velocity, 

 and consequently the vibrations must be stronger or the ridges 

 be weaker or disappear altogether. The refraction of a light 

 through this star produces a very beautiful figure on a screen. 

 120. A heavy tuning-fork vibrating, but not too strongly, if 

 placed with the end of one limb either vertical, inclined, or in 

 any other position, just touching the surface of water, ink, 

 milk, &c. (75), shows the effect very well for a moment. It 

 also shows the ridges on mercury, but the motion and resistance 

 of so dense a body quickly bring the fork to rest. It formed 



