130 ANNUAL KECORD OF SCIENCE AND INDUSTRY. 



were in the first experiment, and not being in time with the 

 vibrations of the other fork, the latter is not affected by them, 

 and the corlv ball remains at rest. But if we now move the 

 weighted fork toioard the other with the proper velocity, 

 then these longer waves will be shortened., and Avill equal 

 those given by the stationary fork, which now enters into 

 vibration and projects the cork ball. The same results are ob- 

 tained when a fork which gives too many vibrations, and there- 

 fore wave lengths, is moved away from the stationary fork. 



These experiments are easily repeated, and can be shown 

 to a large audience by projecting on a screen by means of a 

 lantern the magnified images of the fork and its suspended 

 ball. The experiments beautifully illustrate the well-known 

 method of determining the motions of the heavenly bodies 

 from an examination of the displacement of the fixed lines in 

 their spectra. 



In the second pa^^er. Professor Mayer gives his discovery 

 of a method of detecting the phases of vibration in the air 

 surrounding a sounding body, and thereby measuring directly 

 in the air the lengths of its waves, and exploring the form of 

 its wave surface. To detect the direction of the swinging 

 particles of air, and to describe around a sounding body the 

 form of its wave surfiice, at first seems beyond the reach of 

 experiment, and it was first accomplished by the physicist in 

 the following manner : An organ-pipe has a hole cut in its 

 side ; this hole is then covered with a delicate membrane ; 

 over this membrane is placed a small wooden cup. A gum 

 tube leads into this cup a current of gas, which flows out by 

 another tube, terminated by a small gas jet. When the or- 

 gan-pipe sounds, this gas flame will jump up and down as 

 the membrane closing the mouth of the cup vibrates outward 

 and inward. If we now view this vibrating: flame in a re- 

 volving mirror, it will appear as a band of light, with its 

 upper border cut into teeth like those of a mill-saw, each 

 tooth corresponding to an upward jump of the flame, and 

 each space between two contiguous teeth corresponding to 

 a downward jump of the flame. This method of observing 

 the vibrations of air in an organ-pipe is due to Konig, of Paris. 



If we then take a hollow sphere of brass of the proper size, 

 with a circular opening in one side, and with a small tubular 

 opening in the opposite side (known as a Helmholtz resonator), 



