SCIENTIFIC RECREATIONS. 



accepted as correct. In hydrogen gas the rate is much higher. Through 

 water again it is different, and still faster through iron, glass, and wood, as 

 will be seen in the following table : 



Whalebone . . . 



Tin ...... 7 



Silver ..... 9 



Walnut . . , . I0 



Brass 



TAKING AIR AS i. 



Oak io| 



Earthen pipes . . u 



Copper 12 



Pear- wood . . . \2. 



lof Ebony 143 Deal . . 



Cherry . . . 

 Willow . . 

 Glass . . . 

 Iron or Steel . 



\l 



18 



So there is a considerable difference in the velocities of sound through 

 the solid substances quoted, but these figures cannot be taken as exact, as 

 different samples may give different results. In wires and bells the bodies 

 themselves produce the sounds we hear. In wind instruments and the voice 

 the air is the cause of the sound. 



The very deepest notes are produced by the fewest vibrations. Four- 

 teen or fifteen vibrations will give us a very low note, if not the very lowest. 

 The pipe of sixteen feet, closed at its upper end, will produce sound waves 

 of thirty-two feet. High notes can be formed from vibrations up to 48,000 

 in'a second. Beyond these limits the ear cannot accept a musical sound. 



Fig. 172. The ribration of strings. 



We will explain the phenomenon of the vibration of strings by means of 

 the illustration. In the cut we find a string or wire, which can be lengthened 

 or shortened at pleasure by a movable bridge, and stretched by weights 

 attached to the end (fig. 172). 



We can now easily perceive that the shorter and thinner the string is, 

 and the tighter it is, the number of vibrations will be greater and greater. 

 The density of it is also to be considered, and when these conditions are in 

 the smallest proportion then the tone will be highest. The depth will natur- 

 ally increase with the thickness, density, and length, and with a decreasing 

 tension. But we have strings of same thickness stretched to different 

 degrees of tension, and thus producing different notes. Some strings are 

 covered with wire to increase their gravity, and thus to produce low notes. 



When a number of separate sounds succeed each other in very rapid 

 course they produce a sound, but to appear as one sound to the ear they 

 must amount to fifteen or sixteen vibrations every second. The particles of 

 matter in the air form a connected system, and till they are disturbed they 

 remain in equilibrium ; but the moment they are in any way thrown out of 

 this state they vibrate as the pendulum vibrates. The particles thus strike 



