CHAPTER XVII. 



THE TUNING-FORK THE SYREN SOUND FIGURES SINGING FLAMES. 



WE cannot close the subject of Sound without some mention of the 

 Musical Pitch, and various instruments and experiments which have from 

 time to time been made to discover the pitch, sound, and vibrations, and 

 even to see Sound. To understand the vibrations or " pitch " of a musical 

 note we may study the illustration, which shows us a tuning-fork in vibration. 

 You will perceive that each prong of the tuning-fork beats the air in an 

 opposite direction at the same time, say from a to b (fig. 1 96). The prong 

 strikes the air, and the wave thus created strikes again outward, and the 

 condensation thus created travels along the back beat, rarefying the air, and 



Fig. 196. 



Fig. 197. 



both these, the rarefaction and the condensation, move with the same 

 rapidity one behind the other. 



The tuning-fork of course vibrates a very great many times in a 

 second, every vibration generating a wave. " Pitch," in a general sense, is 

 the number of vibrations per second which constitute a note. For instance, 

 the note A, the standard pitch consists of four hundred and thirty-five 

 complete vibrations per second. Concert pitch is slightly higher, for there 

 are a few more vibrations in the second. The lowest sound pitch is forty 

 vibrations, the highest forty thousand. "Pitch" maybe determined by an 

 instrument termed the "Syren," or by a tooth-wheeled apparatus. 



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