V. VIBRATIONS AND WAVES. 151 



will generate figures such as are caused by the complex effect of the vibra- 

 tions acting at right angles upon one another. By a simple mechanical con- 

 trivance the velocity of the rotary motion of each of the discs can be regulated 

 according to equally simple relative relations, by which the figures of the 

 different intervals are produced. By varying the tension of the strings more or 

 less, an alteration in these places will be achieved. By changing one or the 

 other of these discs, and replacing it by another with a different curve, the 

 figures observed by Dr. Helmholtz, on oscillating strings with the vibration 

 microscope, will be obtained, instead of those of Lissajous. 



Plate II. Two thin rods of steel are fastened by screws at the two 

 oblique corners of a strong bar of iron in such a manner that their further ends, 

 one reaching above the other, vibrate vertically the one upon the other. To 

 these ends small metal plates with incised slits are attached in a parallel 

 position. The reflection of light produced by the intersection of these slits 

 will show Lissajous' figures. A movable weight regulates the intervals. 



B, the well known tuning-fork apparatus with mirrors is simplified by the 

 tuning-fork being replaced by steel springs which are inserted in suitable 

 movable wooden columns. 



Plate III. Apparatus for simplified demonstration. 



A. ramified tuning-fork. 



The same produces a sound composed of two tones, and marks the corre- 

 sponding musical note direct on a smoked glass plate. 



J3, resonator with monometrical flame without membrane. 



A conical shaped Resonator, which is held with the large opening down- 

 wards and is filled from the top with illuminating gas, which is allowed to escape 

 through a small tube attached, and then ignited. The flame will react on the 

 tones in the usual manner. 



C, an igneous Kaleidophon. 



Mr. Tollinger has shown that by fastening with wax a glimmering candle to 

 the end of a prismatic steel spring, a very admirable demonstration for large 

 audiences of this well-known experiment can be produced. 



542 a. Apparatus for combining waves in one plane. The 

 resultant shown is that of two sets of waves (superposed) that 

 differ by half a wave-length. Chas. Brooke, F.R.S. 



542b. Apparatus for combining waves in two planes per- 

 pendicular to each other. The resultant shown is a right-handed 

 elliptic helix. Chas. Brooke, F.R.S. 



1229e. Apparatus for showing the longitudinal vibrations of 

 a row of particles, (1) stationary, and (2) progressive. 



Chas. Brooke, F.R.S. 



The vibrations shown are those constituting the first harmonic subdivision 

 of a pipe closed at one end. 



543. Stationary Liquid Wave Apparatus and Sector 

 Pendulum. Frederick Guthrie. 



When such a system of stationary waves is formed in a deep cylindrical 

 trough that the centre rises and falls as the edge falls or rises, the undu- 

 lation is synchronous with a pendulum whose length is equal to the radius of 

 the trough ; and the accelerations of motion of the wave and pendulum are 

 identical. 



