420 



NOTES. 



NOTE 179, p. 140. Plates 1 and 2 contain a few of Chladnl's figures. 

 The white lines are the forms assumed by the sand, from different modes 

 of vibration, corresponding to musical notes of different degrees of pitch. 

 Plate 3 contains six of Chladni's circular figures. 



NOTE 180, p. 140. Mr. Wheatstone's principle is, that when vibra- 

 tions producing the forms of figs. 1 and 2, plate 3, are united in the same 

 surface, they make the sand assume the form of fig. 3. In the same 

 manner, the vibrations which would separately cause the sand to take 

 the forms of figs. 4 and 5, would make it assume the form of fig. 6 when 

 united. The figure 9 results from the modes of vibration of 7 and 8 

 combined. The parts marked a a are in different states of vibration from 

 those marked b b. Figs. 1, 2, and 3, plate 4, represent forms which the 

 sand takes in consequence of simple modes of vibration ; 4 and 5 are 

 those arising from two combined modes of vibration ; and the last six 

 figures arise from four superimposed simple modes of vibration. These 

 complicated figures are determined by computation independent of experi- 

 ment. 



NOTE 181, p. 140. The long cross-lines of fig. 46 show the two sys- 

 tems of nodal lines given by M. Savart's laminae. 



]Fig. 46. 



LLLU1 



ilLLJ 



NOTE 182, p. 141. The short lines on fig. 46 show the positions of the 

 nodal lines on the other sides of the same laminae. 



NOTE 183, p. 141. Fig. 47 gives the nodal lines on a cylinder, with the 

 paper rings that mark the quiescent points. 



Fiff. 47. 



NOTE 184, pp. 133, 148, 149. Reflection and refraction. Let P C p, 



Fig. 48. 



fig. 48, be perpendicular to a sur- 

 face of glass or water A B. When 

 a ray of light, passing through the 

 air, falls on this surface in any di- 

 rection I C, part of it is reflected 

 in the direction C S, and the oth 

 er part is bent at C, and passes 

 through the glass or water in the 

 direction CR. 1C is called the 

 incident ray, and ICP the angle 

 of incidence ; C S is the reflected 

 ray, and P C S the angle of reflec- 

 tion : C R is the refracted ray, and 

 p C R the angle of refraction. The 

 plane passing through S C and 1 C 

 is the plane of reflection, and the 

 plane passing through 1C and C R 

 is the plane of refraction. In or 

 dinary cases, C I, C S, C B, are all 



