Improvements in Science. 113 



than when not tempered. 3rd, A tuning fork hammered 

 hard gives a longer tone than one heated. 4th, The rapidity 

 of sound appears to be equal in ice and water, at 32°. The 

 experiments of the same author upon the vibration of liquids 

 have been already noticed.* 



4. Pellisorhas endeavoured to form a theory of acoustical 

 instruments. f He considers that the sound consists of the 

 vibration of the molecules, or smallest portions of the 

 sounding body, and not, as Chladni and Weber consider, in 

 the total vibration. He brings forward the following ex- 

 periment to support his position. If we sound one of the 

 strings of an instrument by pulling it in the middle with the 

 fingers, it soon ceases to sound, notwithstanding, it makes 

 vibrations a line broad ; but on the other hand, the tone of 

 the string, when sounded by a tangent force, is very strong, 

 while the vibrations have scarce an appreciable width. 



5. Method of tuning a Guitar without the assistance of the 

 ear.% This method, proposed by M. Bary, professor of 

 Physics, at the Royal College of Charlemagne, in Paris, 

 depends on the circumstance, that the communication of 

 vibratory sounds is most effective through elastic media, 

 when the bodies in the vicinity of the original vibrated 

 body are capable of vibrating in unison with them. When, 

 therefore, two strings fastened near each other possess, for 

 their concord, the necessary tension and length, and one of 

 them is made to sound, the vibrations are, with much 

 force, transferred to the other, and this transference can be 

 made, as Saveur has shown, perceptible to the eye, by 

 placing a saddle of paper upon the string, at first, in a state 

 of rest. When this string hears the other, the saddle will 

 be shaken, and fall off. When both strings are in harmony, 

 the paper will be very little, or not at all shaken. 



6. Effect of Sound on the Barometer. — Sir H. Englefield, 

 while at Brussels, in 1773, made some experiments on this 

 subject. The barometer was fixed in the opening of a window, 

 in the north-east tower of the church of St. Gudule, about 

 7 feet from the summit of the bell. Mr. Pigott found the 

 height of the barometer 29'478 inches. It did not vary 



* Records of General Science, vol. i. 98. 



t Jahrbuck der Chemie and Pnysik, rii. and viii. 



X Pog^emlorff's Amiiilcn, xxxv. 524. 

 VO].. 111. I 



