MUSICAL BAROMETER 65 



tions of two strings, for instance, are performed in equal 

 ti'^ies, the same tone is produced by both, and they are said 

 to be in unison. But concord is not confined to unison ; 

 for two different tones harmonize in a variety of cases. If 

 one string or sonorous body vibrates in double the time of 

 another, the second vibration of the latter will strike upon 

 the ear at the same instant as the first vibration of the for- 

 mer ; and this is the concord of an eighth or octave. If the 

 vibrations of two strings are as two to three, the second vi- 

 bration of the first corresponds with the third vibration of 

 the latter, producing the harmony called a fifth. There are 

 other tones which, though they cannot be struck together 

 without producing discord, yet if struck successively, give 

 us the pleasure which is called melody. 



A sort of musical barometer has been invented in Swit- 

 zerland, called the weather harp, which possesses the sin- 

 gular property of indicating changes of the weather by mu- 

 sical tones. In the year 1787, one was constructed in the 

 following manner. Thirteen pieces of iron wire, each three 

 hundred and twenty feet long, were extended across a garden, 

 m a direction parallel to the meridian. They were placed 

 about two inches apart ; the largest were two lines.>M»dia- 

 meter, the smallest only one, and the others one and a half j 

 they were on the side of the house, and made an aiwle of* 

 twenty or thirty degrees with the hprizon ; -they \v^S> 

 stretched and kept tight by wheels made for that purpose. 

 Every time the weather changes, these wires make so much- 

 noise that it is impossible to continue concerts in the parlouj^ 

 and the sound resembles that of a tea-urn when boilipg, and 

 sometimes that of a distant bell, or an organ. 



QcjESTiONS. — 1. When do the vibrations of a sonorous body pro- 

 duce the same musical tone ? 2. How are discords produced ? 3. On 

 what does the sharpness or acuteness of a musical sound depend ? 4. 

 On what does the duration of tlie vibrations of strings or chords dependji- 

 5. How is harmony or concord produced ? 6. How is an octave con- 

 cord produced ? 7. The harmony called a fifth ? 8. Describeithc 

 musical barometer or weather harp. [Note. In the opinion of -ace- 

 lebrated chemist, this is an electro-magnetical phenomenon.] 9. Illus- 

 trate the vibrations of a musical string by figures 17, 18j and 19. 



6* 



