g26 SPECIAL SENSES. 



freezing-point of water is about 1,090 feet per second. This rate presents comparatively 

 slight variations for the different gases, but it is very much more rapid in liquids and in 

 solids. In ordinary water, it is 4,708 feet per second ; in iron or steel wire, about 16,000 

 feet ; and in most woods, in the direction of the fibre, about the same. 



Noise and Musical Sounds. There is a well-defined physical as well as an aesthetic 

 distinction between noise and music. Taking, as examples, single sounds, a sound be- 

 comes noise when the air is thrown into confused and irregular vibrations. A noise may 

 be composed of a few musical sounds, when these are not in accord with each other, and 

 sounds called musical are not always entirely free from discordant vibrations, as we shall 

 see in studying musical sounds, properly so called. A noise possesses intensity, varying 

 with the amplitude of the vibrations, and it may have different qualities, depending upon 

 the form of its vibrations. We may call a noise dull, sharp, ringing, metallic, hollow, 

 etc., thus expressing qualities that are readily understood. In percussion of the chest, 

 the resonance is called vesicular, tympanitic, etc., distinctions in quality that are quite 

 important. A noise may also be called sharp or low in pitch, as the rapid or slow vibra- 

 tions predominate, without answering the requirements of musical sounds. These expla- 

 nations, with the definition that a noise is a sound that is not musical, will be better 

 understood after we have described some of the characters of musical vibrations. 



A pure and simple musical sound consists of vibrations following each other at regular 

 intervals, provided that the succession of waves be not too slow or too rapid. When the 

 vibrations are too slow, we have an appreciable succession of impulses, and the sound is 

 not musical. When they are too rapid, we recognize that the sound is excessively sharp, 

 but it is then painfully acute and has no pitch that can be accurately determined by the 

 auditory apparatus. Such sounds may be occasionally employed in musical compositions, 

 but, in themselves, they are not strictly musical. 



In musical sounds, we recognize duration, intensity, pitch, and quality. The duration 

 depends simply upon the length of time during which the vibrating body is thrown into 

 action. The intensity depends, as we have already stated, upon the amplitude of the 

 vibrations, and it has no relation whatsoever to pitch. Pitch depends absolutely upon the 

 rapidity of the regular vibrations, and quality, upon the combinations of different tones 

 in harmony, the character of the harmonics of fundamental tones, and the form of the 

 vibrations. 



Pitch of Musical Sounds. In discussing the pitch of musical sounds, we shall leave 

 out of the question, for the present, the harmonics, which exist in nearly all musical notes 

 and affect their quality, and confine ourselves to the study of simple vibrations. Such 

 tones are those of great organ-pipes, which are deficient in harmonics and in overtones, 

 and are almost entirely pure. 



Pitch depends upon the number of vibrations. A musical sound may be of greater or 

 less intensity ; it may at first be quite loud and gradually die away; but the number of 

 vibrations in a definite tone is invariable, be it weak or powerful. The rapidity of the 

 conduction of sound does not vary with its intensity or pitch, and, in the harmonious 

 combination of the sounds of different instruments, be they high or low in pitch, intense 

 or feeble, it is always the same in the same conducting medium. Distinct musical notes 

 may present an immense variety of qualities, but all tones of the same pitch have abso- 

 lutely equal rates of vibration. Tones equal in pitch are said to be in unison. This fact, 

 though simple, has a most important physiological bearing. In the first place, an edu- 

 cated ear can, without difficulty, distinguish slight differences in pitch in ordinary musical 

 tones. Again, we ascertain by experiment that this power of appreciation of tones is 

 restricted within well-defined limits, which vary slightly in different individuals. With- 

 out citing all of the numerous observations upon this point, we may state that Helmholtz, 

 whose authority is the very highest, gives, as the range of sounds that can be legitimately 



