238 TRANSACTIONS OF THE [MAY 21, 
with ‘‘ rockers,” and at times over one hundred men were em- 
ployed. 
Pror. J. 8S. NewBErRRY read, by title, a paper 
ON THE STRUCTURE AND ZOOLOGICAL RELATION OF THE 
PLACODERM FISHES. 
(Published in the Annals, Vol. IV.) 
Dr. L. H. Laupy exhibited and described a new and simple 
form of projecting lantern, and the several kinds of jets and 
illuminants employed. Some discussion followed by Dr. Bolton, 
Prof. Stevens, and Dr. Laudy, regarding the use of zirconia 
pencils in place of lime for the oxy-hydrogen light. The lantern 
was then used in illustrating the subsequent paper by Prof. 
Stevens. 
Pror. W. Le Conte STEVENS read a paper on 
THE QUALITY OF MUSICAL SOUNDS, 
(Illustrated with lantern views.) 
(Abstract. ) 
The elements of a musical sound are pitch, loudness, and 
quality. 
The determination of pitch as an index of rate of periodic mo- 
tion dates back as far as the time of Galileo, whose method was 
naturally crude, in comparison with those of to-day. By means 
of the siren, devised by Cagniard de la Tour, and subsequently 
greatly improved by Helmholtz, and also by other methods 
yet more refined, pitch is quite distinctly measurable, and its 
determination is included among the oft-repeated operations of 
exact science. 
Loudness is appreciable only through sensation, and no means 
for its exact measurement have been thus far devised. It may 
be regarded as at least a function of the energy of vibration, 
which in turn is proportional to the square of the amplitude of 
swing; but this is not a measure of the intensity of the nerve ex- 
citement which involves the sensation of loudness. If an arti- 
ficial membrane be substituted for the ear, the variations of 
energy imparted to it, and manifested to the ear as variations 
of loudness, may be made visible and roughly measured by the 
method of manometric flames. (By means of appropriate lan- 
tern pictures, the construction and use of the manometric cap- 
sule was here shown, and flame images analyzed by the speaker.) 
