[Louvon | A CENTURY OF PROGRESS IN ACOUSTICS 51 
A most important step in advance was made in 1834 by Henri 
Scheibler of Crefeld, who in that year invented his tonometer, con- 
sisting of a series of 56 forks going from A (440) to its octave (880), 
the vibrations increasing regularly by differences of eight, any two 
adjacent forks thus giving four beats per second. Curiously enough, 
although Scheibler went to Paris and exhibited his tonometer there, 
he was unable to interest savants in his discovery; and it was not until 
the London Exhibition of 1862 that the attention of physicists and 
musicians was directed to the value of the instrument by Kenig. The 
apparatus in its new form contained 65 forks going from C —512 
to C= 1024. 
Notwithstanding the great utility of this tonometer to the acous- 
tician, it still left undertermined the absolute pitch of the fundamental 
note, and hence of the whole series. This problem of realizing a 
standard of pitch remained practically unsolved even after the French 
Government in 1859 decreed that the standard should be À — 870 
v.s. at 15 © C. The standard then constructed by Lissajous was found, 
in 1880, to be too high by 9-10 of a vibration. The acoustical standard 
employed: since 1880 by Keenig is C= 512 v.s. at 20°. The acous- 
tical standard before that date was in reality 512.35 at 20°. The 
problem of realizing a standard fork, which had given rise to much 
controversy among physicists, was finally solved in 1880 by Keenig, 
who in that year published his paper “Recherches sur les vibrations d’un 
diapason normal.” In this paper Koenig describes how by means of a 
elock-fork (horloge à diapason comparateur) he established a standard 
fork, the error of which did not exceed 1-6000 of a vibration. The 
clock-fork method enables us at the same time to determine readily 
the variations in the number of vibrations due to a rise or fall of 
temperature. Having established in this way an absolute standard of 
912 v.s. at 20° C., Koenig commenced the construction of a universal 
tonometer based thereon, a colossal undertaking which he finished in 
1897, after working on it for nearly a score of years. This tonometer 
consists of the following: 
1. Four forks giving vibrations from 32 to 128, with differences 
at first of À v.s., and afterwards of 1 v.s. 
?. One hundred and thirty-two large forks, tuned to give (without 
the sliders) the 127 harmonics of c-, — 64 V.8., ©, Ca Cyy C59 Cg being 
in duplicate. Each fork can be lowered, by means of sliders, to unison 
with the fork next below. The differences immediately obtainable by 
sliders are:—1 v.d. between c, and c,; 2 v.d. between c, and ¢,; 4 v.d. 
between c, and c.. 
3. 40 resonators to reinforce forks of (2). 
