of Vibration in the Air surrounding a Sounding Body. 827 



(i; = 7?X) of sound in different gases; for it is easy to close the 

 mouth of the resonator with a delicate membrane, and fill the 

 resonator, capsule, and connecting-tube with various gases; 

 or we can substitute for the resonator a cavity of the proper 

 volume and form, closed by a large membrane which vibrates in 

 unison with the fundamental note of the pipe, and proceed as 

 above. 



It requires but little consideration to see that the measure of 

 a wave-length thus determined greatly exceeds in accuracy those 

 obtained by the method heretofore practised, by which Dulong, 

 Wertheim, and others have reached it indirectly, measuring 

 the internodal distances in sounding pipes ; and the above ar- 

 rangement will, I think, give results even superior in precision 

 to those which we can obtain by the use of the exquisite interfe- 

 rence-apparatus which M. R. Konig has recently described in 

 Poggendorff's ^/i7z«/e7i, vol. cxlvi. p. 165^. 



In my lecture-room I have hung up before the students a 

 series of gum tubes having lengths of J, 1, IJ, 2, 2^, 3, &c. 

 wave-lengths of different notes. These are successively joined 

 to the resonator and its manometric capsule, and they alter- 

 nately produce in the fiames coincidences and bisections of their 

 series of serrations. Students after such exhibitions do not 

 depart from the room with their usual scepticism as to the ex- 

 istence of a sonorous wave-length, but look upon the tubes as 

 measures of actual entities. 



The differences, if any, in the velocities of sounds corre- 

 sponding to vibrations differing in intensity and frequency, may 

 be determined by the use of reflectors and the direct observation 

 of any changes in wave-length different from those which should 

 take place on the assumption that notes of various intensities 

 and heights are propagated with the same velocity. 



Finally, we are bold enough to believe that we have in the 

 highest development of the method a means of tracking in the 

 air the resultant wave-surface of combined notes, and, in short, 

 of bringing the exploration of acoustic space to approach some- 

 what to that precision of measurement which for over half a 

 century has characterized the study of the setherial vibrations 

 producing light. 



September 21st, 1872. 



* [A translation of this paper will appear in one of our next Numbers. 

 Eds. Fhil. Mag.] 



