130 
WEAD. 
holtz’s overtone and resultant-tone theory furnished so strong 
a justification. Perhaps the greatest value of the book has 
been its stimulus to investigation in many fields, especially 
in the psychology of music ; yet in spite of all our modern 
progress the greater part of the work remains as indispen¬ 
sable as ever. 
II. Since the publication of Helmholtz’s work the most 
noteworthy things in connection with Acoustics have been 
these: 
(1.) The multiplying and perfecting of methods and in¬ 
struments, especially by Koenig and Appunn; the develop¬ 
ment and use of the phonograph ; the applications of pho¬ 
tography. 
(2.) The publication of Rayleigh’s mathematical Theory of 
Sound; of the ten volumes of the Vierteljahrsschrift fur Musik- 
wissenschcift, full of scholarly monographs on the musical 
and historical side, and of Ellis and Hipkins’ researches on 
musical scales. 
(3.) The developments in musical instruments (especially 
the piano), so giving us instruments of more accurate intona¬ 
tion and greater power, and unfortunately driving out the 
older, soft-toned instruments. 
(4.) The general introduction into the household of the 
piano or reed organ, often leading psychologically to the con¬ 
viction that there can be no music without harmony. 
(5.) The building up of several great collections of musi¬ 
cal instruments from various lands and times, and the pub¬ 
lication of books and monographs based thereon. 
(6.) The accumulation of a vast amount of observations 
and experiments in the field of music-psychology. 
III. Confining our attention now to Physical Acoustics, 
we may consider a little more in detail some of the recent 
advances that can readily be grouped together. 
The Velocity of Sound in free air has been shown to in¬ 
crease greatly for very intense sounds, and has been meas¬ 
ured in air compressed up to 100 atmospheres. When the 
air is confined in tubes the velocity is found to be a function 
of the diameter and nature of the walls and of the pitch of 
