A. If. Mayer — Sensatioiis of interrupted tones. 283 



course subject to obvious qualification, yet nevertheless they 

 are very helpful toward tangible ideas. The estimates are 

 probably not very accurate but they are representative. 



In the second column, there is shown the amount of excava- 

 tion that took place between the deposit of the high gravels 

 and of the low gravels, in terms of postglacial excavation. The 

 relative importance of these interglacial excavations is strik- 

 ingly manifest. They are represented by two symbols, the 

 one indicating excavation in drift, the other, excavation in 

 rock. The excavation of the cols, which is probably to be 

 regarded as somewhat nearly the same in all cases, is merely 

 indicated as a common factor. In the third column is indicated 

 the valley deposition of the last glacial epoch, which is the 

 unit of deposition, and alike in all cases, and in the fourth 

 column, the postglacial excavation, which is the unit of exca- 

 vation and alike in all cases. 



The import of all these hypotheses is alike on most of the 

 vital points. They all greatly emphasize the importance and 

 significance of the first glacial epoch. This is especially true 

 of the second one. They all show very important intervening 

 excavations when compared with the erosion that has taken 

 place since the glacial period. This is especially true of the 

 first and notably true of the third. They all indicate that, 

 while the last glacial invasion was very much more pronounced 

 in its_ apparent effects and in the ^expression it took on, it was, 

 after all, much the smaller factor of the total accomplishment 

 of the glacial period. 



Art. XXV. — An apparatus to show, simultaneously to sev- 

 eral hearers, the blending of the sensations of interrupted 

 tones ; by Alfred M. Mayer. 



In the January number of this Journal, of the current 

 year, I described several forms of apparatus used in my obser- 

 vations on the frequency of the interruptions of simple sounds 

 required to blend these sounds and obtain from them continu- 

 ous and uniform sonorous sensations. These experiments gave 

 the data of the law connecting the pitch of a sound with the 

 duration of its residual sensation. 



The various apparatus described in that paper are, however, 

 unsuited to exhibit the phenomena to more than one hearer 

 at a time. To enable many hearers to observe simultaneously 

 the phenomena I have devised the apparatus shown in the 

 figure. 



