124 SEC. 4. KINEMATICS, STATICS, AND DYNAMICS. 



5. '\Vith this apparatus an infinite number of combinations can be demon- 

 strated. I will mention only four : 



a. Two vibrations of the same amplitude and velocity, no difference of 



phase. The middle ball has double the amplitude. 



b. The same, the difference of phase being 180. The motion of the 



mid-ile ball is nearly zero. The deviation that will appear results 

 from the difference in the length of BD and CD (Fig. 1). 



c. Combinations of a tone with one of its harmonics 2 and 3 with its 



quint f , or its quart , as well as when they are of the same intensity 

 or not (theory of the timbre). 



d. Combinations of two tones of the same intensity, with the interval if , 



showing the origin of beats. 



541. Apparatus, of a new form, to illustrate Wave Motion. 



C. J. Woodward. 



This apparatus consists of a series of balls suspended from a horizontal 

 beam by strings. These balls rest against a series of partitions in a wedge- 

 shaped horizontal trough, which can be raised and depressed parallel to itself. 

 The box, being drawn on one side in the plane in which the balls hang and 

 then slowly depressed, the balls will be successively liberated, and a wave, 

 similar to that of the sound wave, produced. If the beam be drawn aside 

 prior to depressing the box, the balls will rest against one side of the trough 

 and can be liberated in succession, causing them to oscillate in a plane at 

 right angles to the beam, a vibration being produced similar to that of plane 

 polarized light. 



541a. Wheatstone's Apparatus, for illustrating the com- 

 position of rectangular vibrations. Council of King's College. 



542. Drawings of new Apparatus for demonstrating the 

 composition of Vibrations. Dr. Leopold Pfaundler, Innsbruck. 



Plate I. Two blackened glass discs are each placed on a separate horizontal 

 axis one before the other, in such a manner that the transparent curves 

 apparently cut in their periphery, intersect each other at nearly right angles. 

 A reflection of light is produced thereby, which, at the revolution of the discs, 

 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. Thereby 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 Professor 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 (discs) 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. 



