1880.] Mr S. Taylor, On sound-waves and water-waves. 19 



of equal lengths, each supporting a small wooden ball, are inserted 

 in the wheels perpendicular to their plane near their circumferences, 

 at such points that the phase-difference between any two adjacent 

 balls is one-eighth of a revolution. The balls thus disposed repre- 

 sent two complete equal waves, and, when the winch is turned, 

 the effect of wave-motion is produced. Different positions of an 

 observer's eye with reference to the apparatus lead to the presenta- 

 tion of waves due to different types of particle-movement, both 

 orbital and vibrational. Let the board be first placed with its 

 plane vertical, and with the straight line joining the centres of the 

 wheels horizontal. Let the observer's eye be situated in front of, 

 and at some distance from, the apparatus, in a horizontal plane 

 through the line of centres. Waves due to circular particle-move- 

 ments in the plane of wave-propagation, like those on the surface 

 of deep water, are now seen. The observer's eye remaining sta- 

 tionary, let the board be next gradually turned about the line of 

 centres. The circles are thus projected into ellipses with major 

 axes horizontal, such as give rise to water-waves below the sur- 

 face. These degenerate, when the plane of the board becomes 

 horizontal, into straight vibrational paths in the direction of pro- 

 pagation, harmonically described, and giving rise to waves like 

 those of a sound of one degree of pitch, or ' simple tone.' By 

 suitably altering the position of the observer's eye in the plane on 

 which it is situated, these paths can be made to look as if executed 

 obliquely to the direction of wave-propagation. Lastly, replacing 

 the board in its original position, let it be gradually turned about 

 a vertical axis on its own plane. The circles then pass into ellipses 

 with vertical major axes, degenerating ultimately into straight 

 lines transverse to the direction of wave-propagation, and thus 

 presenting the case of plane-polarized light. All the types of 

 wave-motion ordinarily requiring illustration, with the exception 

 of circularly and elliptically polarized light, are, therefore, capable 

 of being represented by this apparatus. 



November 22, 1880. 



Professor Newton, President, in the Chair. 



C. Creighton, M.A., Demonstrator of Anatomy, was balloted 

 for and duly elected a Fellow of the Society. 



The following communications were made to the Society : 



(1) On the experiments made by Blot and others on horizontal 

 refraction. By J. B. Pearson, D.D., Fellow of Emmanuel College. 



I was led to investigate this question by some remarks made 



