254 AKNTJAL REPORT SMITHSONIAN INSTITUTION, 1953 



sweep through the whole gamut of frequencies to obtain an acoustic 

 spectrum whereon we have the loudness of the component frequencies 

 of the individual tones which make up a certain note exhibited by the 

 heights of the peaks standing over those frequencies. 



For unsteady notes such as the transients that accompany the start- 

 ing of a note, we commonly exhibit the wave form on a cathode-ray 

 oscillograph. Here the electron beam is made to inscribe the wave 

 form on the screen in the same way that the gramophone needle does 

 on the plastic disk, or the light spot on the sensitive film when activated 

 by the sound. A short portion of the oscillograph record (of which 

 I will give examples later) is then turned into one of the "hill-and- 

 dale" type, and fastened round the rim of a heavy wheel (pi. 1, fig. 1) 

 so that when the latter is rotated the film passes between a pea lamp 

 and a photoelectric cell, the current of which is passed to a vibration 

 galvanometer of 50 c/s natural frequency. (This is a development 

 of an apparatus which I also described in the 1940 lecture.) The 

 wheel, having been spun by an electric motor up to a considerable speed, 

 is allowed to come to rest slowly so that the galvanometer responds 

 each time the rate of rotation momentarily causes the light beam to 

 be interrupted by the film at the rate — i. e., 50 times a second— to 

 which the galvanometer is tuned. In this way the component fre- 

 quencies at various instants during the commencement or dying away 

 of a note, e. g., of a bell, may be established. 



But enough of technical details, let us turn to results. I will first 

 discuss what has come to light about the acoustics of the orchestra 

 in a general way and then pass in rapid survey over information 

 peculiar to the chief types of instruments. 



THE ORCHESTRA AS A WHOLE 



The complex subjective processes which we call listening to music 

 involves the three P's of science : physics, physiology, and psychology. 

 Although the aspects of musical acoustics with which we are concerned 

 in the laboratory or instrument factory are mainly physical, they do 

 not comprise by any means the whole process of musical appreciation, 

 and he who supposes that physics is the only "science of music" would 

 err in the same fashion as he who reduces the art of Bach to a set of 

 rules regarding the resolution of discords, related keys of subject and 

 answer in fugues, etc., and the like. 



One question may properly be answered in physical terms merely : 

 that is, how the sounds of one instrument, played solo, may be dis- 

 tinguished from those of another. Every musician knows that this is 

 mainly a question of timbre, which means the number and magnitude of 

 the overtones (harmonic or inharmonic) which accompany the funda- 

 mental or nominal note which the player intends to produce. The 



