SECTION 13. GENERALISATION OR EXTENSION. \\\ 



single and multiple, are the result of the reflection of the vibra- 

 tions by a spacious obstacle at a certain distance, in certain 

 circumstances ; and resonance results from conditions where the 

 sounds are strengthened or reinforced. 4. Sounds often tend 

 to continue beyond the action which gave rise to them, because 

 they are due to the vibration of objects (as when we have 

 ceased striking a bell with a hammer). 5. Sound waves, and 

 therefore sounds, travel far more slowly than light waves 

 (1,120 feet against 186,000 miles per second!); hence the flash 

 from a distant gun at night reache's us some time before the 

 connected explosion is heard. 6. Sound waves are quickly ex- 

 hausted; hence ordinary sounds in an ordinary medium are 

 only heard from a short distance, say up to a quarter of a 

 mile, and no sounds are distinguished beyond (say) 50 miles. 



7. The exhaustion of sound waves is gradual; hence sounds 

 fade with distance, detail and diversity gradually passing away. 



8. Hence, per contra, only those infinitely few sound waves and 

 sounds reach us which emanate from comparatively near objects, 

 excluding some exceptional sounds of great violence. 9. Sound 

 waves, and therefore sounds, are also liable to deflection, and 

 hence a strong wind, according to its direction, favours or 

 opposes sounds reaching us. 10. Non-periodic and periodic 

 sound vibrations are said to account for "noise" and "har- 

 mony". 11. Sound waves, and therefore sounds, are only par- 

 tially affected by most intervening objects, such as windows 

 or walls. 12. Sound waves, and therefore sounds, interfere and 

 fuse with one another (e. g., a band playing). 13. Loud sounds, 

 as in a busy thoroughfare, "drown" low ones, and great stillness, 

 as at night, contributes to the discernment of comparatively 

 very low sounds. 14. Sound waves of no more than about 

 50 vibrations and over about 20,000 vibrations, are inaudible. 

 15. The world of sound is sometimes given in a co-existing 

 and successive series (e.g., a concert). 



C. OBJECTS.l. Sounds emanate from objects. 2. Sounds 

 normally represent objects as a whole in their three dimensions, 

 and not, as with sight, surfaces only. (Note being in a room, 

 and hearing some one on the floor above stamp his feet the 

 whole thickness of the ceiling is involved.) 3. Sounds deal 

 with objects in motion, molecular and molar, there being usually 

 two objects concerned, the one acting, the other acted upon; 

 but in the case of wind, for instance, the object and the medium 

 are identical. 4. The source of sound in objects is a vibratory 

 motion sometimes visible, sometimes palpable, also illustrated 

 by 2. 5. Comparative voluminousness of bodies vibrating 

 explains massiveness and fineness of sound. 6. Sounds vary 

 according to the varying composition of objects. 7. In propor- 

 tion to the energy of a movement or vibration, sound is per- 

 ceived from a shorter or longer distance. 8. Sounds differ with 

 consistency, size, shape, and other physical qualities of sub- 



