ACOUSTICS AND GRAVITATION. 



37 



4K. cm, 



32. Closed organ-pipe. The tubes heretofore studied were all relatively 

 narrow, so that only the overtones strongly responded on blowing. It is 

 therefore desirable to examine a relatively wide pipe p, figure 56, inset (di- 

 ameter 2.6 cm., length to the telephone plate 13 cm., smooth brass) , from which 

 a strong fundamental (#c") could be easily obtained. The brass pipe was 

 attached with cement, axially to the mouth of the telephone T. An exami- 

 nation both as to frequency (at 12 cm. below the mouth) and depth distri- 

 butions of pressure, made with the pin-hole probe s, is given in the graphs 

 of figure 56. With the exception of the small supernumerary maximum at the 

 sharp a', the pressure relations are simple, there being only one strong, abrupt 

 maximum at %c" coinciding with the blown note, within the range (e 1 to a") 

 surveyed ; but the suggestion of a second maximum 



near c'" (which could not be reached) is obvious. 

 There were no dilatations. 



This distribution in depth is also a smooth curve 

 which begins with a significant value in the plane of 

 the mouth of the tube, and reaches a maximum a few 

 millimeters from the telephone plate. The high 

 pressure value (0.012 cm. of mercury) in this wide 

 pipe is remarkable, as there were 1,000 ohms in the 

 telephone circuit. 



33. Open pipes and adjutages. The final experiments were made with 

 an adjutaged open pipe pp, 33 cm. long and 3 cm. in diameter, blown by tele- 

 phone T, as shown by the inset in figure 57. The adjutage or connecting-pipe 

 a (7.5 cm. long and over i cm. in diameter) was screwed in at both ends and 

 cemented. The pipe pp had a hole (diameter 0.6 cm.) opposite a, through 

 which the long pin-hole probe s (aluminum or glass quill-tube) could be in- 

 serted to any depth; or, again, the probe could be introduced into the pipe pp 

 longitudinally to any depth, as shown at s', the lateral hole being either left 

 open or closed with a cork. A short flexible tube connected 5 or 5', with either 

 (closed) reservoir of the U-tube, the other having been opened to the atmos- 

 phere. It is interesting to note that if the two halves of the pipe pp are not 

 equally long, measured from a, or if the notes are not harmonics, the telephone 

 evokes violent beating wave- trains from the two ends of pp. 



The survey was first made in the adjutage a within a few centimeters of the 

 telephone plate, with results as in the two graphs given in figure 57. Not- 

 withstanding the complication of these examples, both are in agreement 

 and both pressure increments and decrements occur, particularly in the lower 

 curve. As there are 5 maxima and as many minima, often close together, it 

 seems probable that the harmonics of the open pipe are here superimposed on 

 those of the adjutage. 



The pipe pp responded to the note a' when the cork opposite the adjutage 

 was in place, and to d" (flatted) when the cork was out. Both cases were 

 studied. The d" pipe showed but this single maximum between g r and a" and 



