( 710 ) 
5. The minimum perceptible during the unity of time may be 
fixed by the scale (Minkema x )). 
6. The limit of distinction may be traced and the typical variation 
it undergoes in the scale (Deenik ! )). 
7. The sensation of a report, observed by Hensen at a sudden 
intonation or interruption of siren-tones, may be demonstrated in 
tones of different origin and pitch, with the aid of a sudden opening 
or closing of a telephone-contact or a sudden opening or closing of 
a particularly constructed lead cock. 
8. The spreading of the sound round a tuning-fork with the 
situation of the well-known interference-planes may be accurately 
traced, without making the mistakes that must necessarily arise in 
apartments with echoing walls. 
9. The action of the winding mollusc-shells as to their resonance 
for buzzes may be proved directly. 
10. The sound-extinguishing action of different means of isolation 
may be traced with perfect security; for reports by dropping steel 
balls on a steel plate 3 ) (fall-phonometer of Zoth), for tones by electri¬ 
cally touching purely tuned bells; in both cases the instrument put 
in a small non-resonant space; the walls of this space are covered 
with the materials that are to be examined, and, on the one side 
the energy with which the bells are touched, and on the other the 
distance at which the sound is heard, is defined; the completes! 
isolation with an equal thickness of the walls is got in the case of 
trichopiese, then follows the peatmoss-plate from Klazienaveen, then 
the corkstone; other materials that we examined had a considerably 
smaller sound-extinction. 
2 ) H. F. Minkema, Onderz. Physiol. Lab, (5) VI. p. 134. 
2 ) Meeting of this Academy 3 Nov. 1905. 
elVpi^of te,d Prerent reS ° nanCe lLe Slale P Ialc has to be soldered upon a 
