ACOUSTICS. 



63 



form a shaded net-work of singular beauty. Drawing 

 the bow so as to produce notes of different pitch, the 

 waves will be large or small as the notes are low or 

 high, and with a mixed note it is possible to get two or 

 more systems superposed. 



If a common tuning-fork be struck and then have 

 one of its prongs put in contact with the surface of the 

 water in this tank, a beautiful radiation of ripples may 

 be seen, resembling somewhat the arrangement of iron 

 filings about the poles of a magnet. The motion of 

 water in a shallow bell-glass can be projected by letting 

 the parallel beam from the vertical lantern go through 

 it, doing away with the condenser, as the vessel itself 

 would act as a lens if water were in it. The bow may 

 be drawn across its edge when it will give out a musical 

 sound, the water will be thrown into ripples, and a large 

 objective might be used to project the whole surface. 

 The bell-glass may be filled with ether or alcohol, and 

 then sounded. Some of the liquid assumes the sphe- 

 roidal form, and these are driven over the surface to the 

 nodal lines. (See Tyndall on Sound.) 



MANOMETRIC FLAMES. 



The flame of a candle, or lamp, or gas-jet, if a lumin- 

 ous one, can be projected upon a screen by using a 



concave mirror 

 (Fig. 40). It 

 will be invert- 

 ed and magni- 

 fied. If while 

 the flame is 

 projected the 

 mirror be tilted 

 Fig, 40, so as to swing 



