438 



SWAN. 



Results. 



The results are summarized in Table 3. Following Wien, the 

 logarithm of the reciprocal of the minimum energy is used as an index 

 of the sensitivity. In Figure 2, these sensitivity values are plotted 

 against the pitch. Curve 1 shows the result of the present work. 

 Curve 2 shows Wien's final work, and Curve 3 shows that of Fletcher 

 and Wegel. The scattering results of other investigators are also 

 indicated. 



TABLE 3. 



It will be noted that the energy values of the present investigation 

 are somewhat smaller than those obtained by Rayleigh and lie very 

 near the earlier results of Wien, but are considerably larger than 

 Wien's later determinations. This is not surprising as we have 

 already seen that the work of early experimenters was carried on under 

 conditions lacking in quiet which would give too large results, while 

 the later work of Wien is open to criticisms quite as serious operating 

 in the opposite direction. 



It is a surprising fact that, in all previous investigations either by 

 physicists or psychologists, the assumption has been made that the 

 sound energy is propagated in spherical or hemispherical waves, obey- 

 ing the law of inverse squares. Such an assumption is unjustifiable 

 even in experiments conducted out-of-doors, owing to the porosity 

 of the surface of the ground which absorbs the energy and alters its 

 distribution. In a closed room, the sources of error are multiplied on 

 account of reflection from the walls, and here lies the principal criti- 

 cism to be applied to the later work of W ien. 



No matter how small the amount of energv emitted by a source in a 

 closed room, the wave will be reflected from surface to surface many 



