ACOUSTICS AND GRAVITATION. 33 



The rubber tube was now about halved in length, the present depth to plate 

 being about 5 cm. and the diameter 0.75 cm. The note obtained with the 

 blower was a faint d' and a strong g" . The survey in pitch with the pin-hole 

 at a depth of 4 cm. is shown in figure 50, 700 ohms being in circuit. There are 

 maxima at d' and particularly at the octave of the blown pipe d" 1 and minima 

 at e' and a', all well marked. If we compare the present curve for the half 

 pipe with figures 45 and 46 for the full pipe (remembering that the latter curve 

 is inverted), there is thus a complete inversion of results, maxima taking the 

 place of minima. Adding the discarded part of the tube, the results of figure 45 

 were reproduced; but on adding a part but i cm. shorter, the curve corre- 

 sponded in character to figure 50, though with less displacement throughout. 

 Hence a little difference in length, possibly with some incidental difference in 

 width, may change pressure increments into decrements and greatly modify 

 the sensitiveness. 



Figure 50 also shows the effect of the depth of the pin-hole below the mouth 

 of the tube, on the fringe displacements 5, for the d" maximum. The largest 

 displacement occurs at about 5 mm. from the plate. 



29. Pressures in smooth straight pipes. The simple results for these pipes, 

 given in figure 49, seemed to me suspicious, and possibly referable to a dete- 

 rioration of the pin-hole valve after prolonged use. Thus, even a slight ad- 

 ditional sound leak, or looseness, would contribute to such simplification. 

 The pin-hole was therefore carefully overhauled and the survey of the straight 

 tube (13 cm. deep, i cm. diameter) between f' and g" repeated with results 

 recorded (pressures now laid off positively) in figure 51. The suspicion was 

 thus well founded; for the sensitiveness in the present results is enormously 

 greater than in the case figure 49, so that even 100 ohms placed in the tele- 

 phone circuit do not keep the fringes within the limits of the field. As I did 

 not wish to replace the ocular micrometer by the slide-micrometer because 

 of the danger of complications, most of the curves are open at the dilatation d". 



The present curves (fig. 51) therefore reproduce faithfully the pressure 

 minima near f and d", and the pressure maxima near a' and possibly c" of 

 figures 45 and 46, though on a much larger scale, with the exception of the 

 latter (c"), which in both figures is uncertain; but the character of the results 

 is the same for the rough and the smooth tubes, in spite of a difference in bore 

 (0.75 cm. and i.oo cm.). Finally, the smooth tubes respond to a' when blown. 

 The harmonics d" and c", which are supernumerary here, however, also occur 

 in figure 42, for the resonator R' (IV) alone, with corresponding intensity and 

 sign. These must therefore arise in something which has not changed, i. e., in 

 the telephone itself one might surmise, or even in the resonator, cut off though 

 it is by the pin-hole valve. 



In the inset (a' at 100 ohms) I have laid off the fringe displacement 5 in its 

 variation with the depth of the pin-hole below the mouth of the tube. This 

 could not be done at d", since the curves are here incomplete. As these con- 

 trasting distributions are, however, of great interest, I made a set of inde- 



