74 PROCEEDINGS OF THE AMERICAN ACADEMY. 



of a portable apparatus shown in Figure 5. The reduction of these 

 results on the following day showed variations indicative of maxima 

 and minima, which to be accurately located would require the de- 

 termination of intermediate points. The experiment the following 

 night was by means of the organ shown in Figure 6, and points were 

 determined for the E and G notes in each octave between C2 128 and 

 Ce 2048. Other points would have been determined, but time did not 

 permit. It is obvious that the intermediate points in the lower and 

 in the higher octave were desirable, but no pipes were to be had on 

 such short notice for this part of the range, and in their absence the 

 data could not be obtained. In the diagram. Figure 7, the points 

 lying on the vertical lines were determined the first night. The 

 points lying between the vertical lines were determined the second 

 night. The accuracy with which these points fall on a smooth curve 

 is perhaps all that could be expected in view of the difficulty under 

 which the observations were conducted and the limited time available. 

 One point in particular falls far off from this curve, the point for C3 256, 

 by an amount which is, to say the least, serious, and which can be jus- 

 tified only by the conditions under which the work was done. The gen- 

 eral trend of the curve seems, however, established beyond reasonable 

 doubt. It is interesting to note that there is one point of maximum 

 absorption, which is due to resonance between the walls and the sound, 

 and that this point of maximum absorption lies in the lower part, 

 though not in the lowest part, of the range of pitch tested. It would 

 have been interesting to determine, had the time and facilities per- 

 mitted, the shape of the curve beyond C7 4096, and to see if it rises 

 indefinitely, or shows, as is far more likely, a succession of maxima. 

 The scale employed in this curve is the same as that employed in the 

 diagram of the unpainted and painted wall surfaces. It may perhaps 

 be noted in this connection that at the very least the absorption is four 

 times that of painted brick walls. 



The experiment was then directed to the determination of the absorp- 

 tion of sound by cushions, and for this purpose return was made to the 

 constant temperature room. Working in the manner indicated in the 

 earlier papers for substances which could be carried in and out of a 

 room, the curves represented in Figure 8 were obtained. Curve 1 

 shows the absorption coefficient for the Sanders Theatre cushions, with 

 which the whole investigation was begun ten years ago. These cush- 

 ions were of a particularly open grade of packing, a sort of wiry grass 

 or vegetable fiber. They were covered with canvas ticking, and that 

 in turn with a very thin cloth covering. Curve 2 is for cushions bor- 

 rowed from the Phillips Brooks House. They were of a high grade, filled 



