180 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



gan-Luilder of Cologne, has thoroughly examined this sub- 

 ject, and has come to quite a different conclusion. He states 

 that when a pipe is sounded, the blast being so arranged as 

 to brush the upper lip of the pipe, the current thus produced 

 carries continually out with it air particles from the interior 

 of the pipe, the particles of course being those which lie 

 nearest to the opening. Though a small portion of the cur- 

 rent in passing to the lip goes into the pipe, yet the quan- 

 tity of air which the current pulls out is considerably great- 

 er. Hence then arises, first of all, a rarefaction in the lower 

 layer of air in the pipe. The exterior air now seeks to bal- 

 ance the rarefaction, but it can not at once reach it, either by 

 the upper or the lower opening of the pipe. The air-column 

 at rest in the pij^e only yields to the outer atmospheric press- 

 ure when the rarefaction has extended to the middle of the 

 pipe, where in the fundamental note of an open pipe the node 

 is formed. At the lower opening of the pij^e the blast cur- 

 rent of course closes the aperture, and prevents the equilib- 

 rium there. Now at the moment in which the rarefaction 

 in the lower part of the pipe has reached such a degree that 

 the pressure of the external air is able to press the blast cur- 

 rent inward, an air wave is cut off from the blast current at 

 the upper lip, and a small momentary condensation is the re- 

 sult. This wave is propagated along the pipe, and at the 

 middle it collides with the condensed wave which the press- 

 ure of the external air has simultaneously produced in the 

 upper opening of the pipe or the air-column. Thus in the 

 middle of the tube is formed a strong condensation, which 

 may be called tlie acoustic wave, since from that time forth 

 the peculiar vibration of the column and the phenomenon of 

 sound are produced. It is evident, moreover, that at the 

 moment when an air wave has detached itself from the blast 

 current, and has removed the rarefaction in the lower part 

 of the pipe, the blast current returns to its former condition 

 or direction, and produces again its effect upon the air in the 

 pipe. Again a rarefaction is produced, the blast current is 

 again pressed inward, and with the consequent condensation 

 the return of the acoustic wave of the node of vibration co- 

 incides. Thus the hypothetical impulses heretofore assumed 

 are resolved into a pendulous oscillation of the blast current, 

 which has its greatest amplitude at the edge of the upper lip, 



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