with long curly hair, and covered with canvas ticking, which was in turn covered by a long nap plush. Curve 3 is for the cushions of Ap

The absorbing power of cushions. Curve 1 is for "Sanders Theatre" cushions of wiry vegetable fibre covered with canvas ticking and a thin cloth. Curve 2 is for "Brooks House" cushions of long hair covered with the same kind of ticking and plush. Curve 3 is for " Appleton Chapel" cushions of hair covered with ticking and a thin leatherette. Curve 4 is for the elastic felt cushions of commerce of elastic cotton covered with ticking and short nap plush. The absorbing power is per square meter of surface. C (middle C) 256.

pleton Chapel, hair covered with a leatherette, and showing a sharper maximum and a more rapid diminution in absorption for the higher

frequencies, as would be expected under such conditions. Curve 4 is probably the most interesting, because for more standard commercial conditions. It is the curve for elastic felt cushions as made by Sperry and Beale. It is to be observed that all four curves fall off for the higher frequencies, all show a maximum located within an octave, and three of the curves show a curious hump in the second octave. This break in the curve is a genuine phenomenon, as it was tested time after time. It is perhaps due to a secondary resonance, and it is to be observed that it is the more pronounced in those curves that have the sharper resonance in their principal maxima.

Observations were then obtained on unupholstered chairs and settees. The result for chairs is shown in Figure 10. This curve gives the absorption coefficient per single chair. The effect was surprisingly small; in fact, when the floor of the constant temperature room was entirely covered with the chairs spaced at usual seating distances, the effect on the reverberation in the room was exceedingly slight. The fact that it was so slight and the consequent difficulty in measuring the coefficient is a partial explanation of the variation of the results as indicated in the figure. Nevertheless it is probable that the variations there indicated have some real basis, for a repetition of the work showed the points again falling above and below the line as in the first experiment. The amount that these fell above and below the line was difficult to determine, and the number of points along the curve were too few to justify attempting to follow their values by the line. In fact the line is drawn on the diagram merely to indicate in a general way the fact that the coefficient of absorption is nearly the same over the whole range. A varying resonance phenomenon was unquestionably present, but so small as to be negligible; and in fact the whole absorption by the chairs is an exceedingly small factor. The chair was of ash, and its type is shown in the accompanying sketch, Figure 9.

The results of the observations on settees is shown in Figure 11. Those plotted are the coefficients per single seat, there being four seats to the settee. The settees were placed at the customary distance. Here again the principal interest attaches to the fact that the coefficient of absorption is so exceedingly small that the total effect on the reverberation is hardly noticeable. Here also the plotted results do not fall on the line drawn, and the departure is due probably to some slight resonance. The magnitude of the departure, however, could not be determined with accuracy because of the small magnitude of the total absorption coefficient. For these reasons and because the number of points was insufficient, no attempt was made to draw the curve through the plotted points, but merely to indicate a plotted tendency. The

The absorbing power of ash settees shown in Figure 9. The absorption is per

single seat, the settee as shown seating five.

settees were of ash, and their general style is shown in the accompanying sketch.

An investigation was then begun in regard to the nature of the process of absorption of sound. The material chosen for this work was a very durable grade of felt, which, as the manufacturers claimed, was all wool. Even a casual examination of its texture makes it difficult to believe that it is all wool. It has, however, the advantage of being porous, flexible, and very durable. Almost constant handling for several years has apparently not greatly changed its consistency. It is to be noted that this felt is not that mentioned in the papers of six years ago. That felt was of lime-treated cow's hair, the kind used in packing steam pipes. It was very much cheaper in price, but stood little handling before disintegrating. The felt employed in these experiments comes in sheets of various thicknesses, the thickness here employed being about 1.1 cm.

The coefficient of absorption of a single layer of felt was measured for the notes from C1 64 to C, 4096 at octave intervals. The experiment was repeated for two layers, one on top of the other, then for three, and so on up to six thicknesses of felt. Because the greater thicknesses presented an area on the edge not inconsiderable in comparison with the surface, the felt was surrounded by a narrow wood frame. Under such circumstances it was safe to assume that the absorption was entirely by the upper surface of the felt. The experiment was repeated a great many times, first measuring the coefficient of absorption for one thickness for all frequencies, and then checking the work by conducting experiments in the other order; that is, measuring the absorption by one, two, three, etc., thicknesses, for each frequency. The mean of all observations is shown in Figure 12 and Figure 13. In Figure 12 the variations in pitch are plotted as abscissas, as in previous diagrams, whereas in Figure 13 the thicknesses are taken as abscissas. The special object of the second method will appear later, but a general object of adopting this method of plotting is as follows:

If we consider Figure 12, for example, the drawing of the line through any one set of points should be made not merely to best fit those points, but should be drawn having in mind the fact that it, as a curve, is one of a family of curves, and that it should be drawn not merely as a best curve through its own points, but as best fits the whole set. For example, in Figure 12 the curve for four thicknesses would not have been drawn as there shown if drawn simply with reference to its own points. It would have been drawn directly through the points for Similarly the curve for five thicknesses would have been drawn a little nearer the point for C, 128, and above instead of

C1 64 and C2 128.

below the point for C1 64. Considering, however, the whole family of curves and recognizing that each point is not without some error, the

The absorbing power of felt of different thicknesses. Each piece of felt was 1.1 cm. in thickness. Curve 1 is for a single thickness, curve 2 for two thicknesses placed one on top of the other, etc. As shown by these curves, the absorption is in part by penetration into the pores of the felt, in part by a yielding of the mass as a whole. Resonance in the latter process is clearly shown by a maximum shifting to lower and lower pitch with increase in thickness of the felt. Cs (middle C) 256.

curves as drawn are more nearly correct. The best method of reconciling the several curves to each other is to plot two diagrams, one in which the variations in pitch are taken as abscissa and one in which