THE HAMILTON ASSOCIATION. 51 
RESUME, 
1. Sound is the result of air vibrations being transmitted to 
the brain by the ear drum. 
2. Musical sounds are the result of regular vibrations, noise of 
irregular. 
3. Air-vibrations are started by vibrating string, reed or fork, 
but need reinforcing by sound-boards or resonance chambers in 
order to travel far. 
4. Organ pipes stopped at the upper end sound an octave 
lower than pipes of the same length open. 
5. Pitch of sound depends on length (or frequency) of air 
waves ; loudness or amptitude, on width of waves ; quality, on the 
presence of overtones in varying strength ; or, in other words, on 
the shape of the waves. 
6. Sound travels, roughly speaking, 1140 feet per second, a 
mile in nearly five seconds ; light at 200,000 miles per second. 
7. Sound travels feebly in varied air or light gas such as 
hydrogen. 
8. Sound is not hindered but rather assisted by fog or 
dampness. 
g. Strata of unhomogeneous air will destroy the carrying 
power of sound. 
ro. Sound travels four times as quickly in water as in air, 17 
times as quickly as in iron, 10 times as quickly along pine fibre, 
because the elasticity is much greater in proportion to their density. 
11. The Siren proves that the pitch of a sound depends on the 
frequency or number per second of its vibrations. A sound makes 
twice the number made by a sound an octave lower. 
12. The lowest note audible to the human ear has about 16 
vibrations per second ; the highest 38,000. 
13. Vowel-sounds are merely varieties of quality or “ timbre,” 
and as such depend on the presence and varying strength of certain 
overtones. 
