204 
together with the measure of intensity- 
discrimination, should correlate well with 
the measure of the perception of intensity 
in rhythm-accent. 
In the survey of the motor capacity of 
the singer, we naturally follow the same di- 
visions, according to the attributes of tones, 
as in the sensory; namely, pitch, intensity 
and duration of tones. There are four 
fundamental phases of simple pitch sing- 
ing which should be examined separately: 
(1) simple ability to reproduce the pitch 
of a tone heard one second before the sing- 
ing; (2) the ability to make faint shadings 
(sharp and flat) in pitch, (3) the ability to 
sing intervals, and (4) the ability to sus- 
tain a tone, both with reference to periodic 
and progressive changes in pitch. The 
record of the ability to sound the pitch of 
the tone should be taken at ec’, 256 vd., and 
at points near the upper and the lower 
limits of the musical register of the voice. 
The voluntary control of the pitch of the 
voice, measured in terms of the minimal 
producible, sharp or flat, should all be re- 
corded at the same three points in the reg- 
ister. The measure of ability in singing 
intervals should be taken (a) for two or 
three relatively pure intervals near the 
middle of the register of the voice, (6) for 
the singing of the natural scale, and (c) 
for the singing of the chromatic scale. 
The ability in the sustaining of the pitch 
of a tone for ten seconds may also be meas- 
ured at the three representative levels of 
the register and should be so recorded as 
to show both progressive and periodic 
changes. Progressive changes are tenden- 
cies to gradually sharp or flat: periodic 
changes may be either regular or irregular 
oscillations in pitch, or a general lack of 
control. 
The register of the voice should be 
stated in terms of the characteristic changes 
in timbre which take place near the upper 
SCIENCE ° 
[N.S. Vou. XXXV. No. 893 
and the lower limits. Thus we may de- 
termine the range for agreeable musical 
tones, for tones easily sung, for chest tones 
and for true pitch singing. This series of 
records should be supplemented by a 
systematic description of the progressive 
change in the character of the tone from 
one end of the register to the other. 
Under the head of timbre of the voice, 
the psychological-esthetic effect we seek to 
establish is the degree of beauty of the ob- 
jective tone. We therefore eliminate sub- 
jective and circumstantial conditions and 
accessory features of the singing which may 
modify the agreeableness and disagreeable- 
ness of the given tone and consider only 
beauty as it is objective in the physical 
tone. This may be measured with consid- 
erable precision in terms of the form of the 
sound wave. From a single, well-chosen, 
graphic record of the voice, we may work 
out the following factors: (a) purity, the 
degree of approach to the smooth sine curve 
in the form of the wave; (0b) richness, the 
number of overtones present; (c) mellow- 
ness, the character of the distribution of 
the overtones; (d) clearness, the uniform- 
ity in the form of a series of waves; (e) 
flexibility, the character of the progres- 
sive transition from one wave form to 
another. These purely objective measures 
of the beauty of the tone must be supple- 
mented by systematic observations on the 
agreeableness of the timbre of the voice by 
experts judging separately each of the 
specific qualitative aspects of the voice as 
naturally used in singing. Objective 
record must also be made on the mode of 
tone production, especially characteristics 
of the resonance. 
The plasticity of the individual in a 
given capacity is measured by the rate and 
character of the learning processes in that 
capacity. We now know enough about the 
characteristics of learning curves to be able 
