thing—of the waves produced in the medium. Second, the timbre, or quality, which is regulated by the shape, or outline, of these waves. Third the pitch, high or low, which is controlled by the distance from crest to crest of the sound-waves—or, as we say, from node to node of the vibrations.
To the most sensitive human ear, the highest limit of audibleness is reached by sound-waves estimated at twenty-eight-hundredths of an inch from node to node—equal to 48,000 vibrations per second. The extreme of lowness to which our sense of hearing is susceptible, has been placed at 75 feet from node to node—or 15 vibrations per second. This total range of audibleness covers 12 octaves; running, of course, far above and far below the domain of music. The extreme highness and lowness of sounds which convey musical impression are represented, respectively, by 2,000 and by 30 vibrations per second—or by sound-waves, in the former case, of 61⁄2 inches, and in the latter, of 371⁄2 feet.
Therefore, there are not only sounds which by reason of highness or lowness are unmusical, but, beyond these, others to which the tympanum of the human ear is insensible. Nature is alive with such sounds, each carrying its three distinct properties of intensity, timbre and pitch; but whilst this muddy vesture of decay doth grossly close us in, we can no more hear them than we can hear the 'music of the spheres'—apt term for that celestial harmony of motion which guides the myriad orbs of the Universe in their career through Space. But, to take an illustration from the visual faculty: any sound beyond the highest limit of audibleness would resemble a surface lined so minutely and closely as to appear perfectly plain; whilst a sound too low in pitch to be heard would be represented by superficial undulations of land or water so vast in extent that the idea of unevenness would not occur. We have fairly trustworthy evidence that whales communicate with each other by notes so low in pitch—by sound-vibrations so long in range, so few per second—that no human ear can detect them. Bats, on the other hand, utter calls so high—producing such rapid pulsations—as to be equally inaudible to us
Unison of musical notes is attained when the respective numbers of pulsations per second admit a low common-divisor. For instance, the note produced by 60 vibrations per second will chord with one produced by 120—each node of the former coinciding with each alternate node of the latter. 60 and 90 will also chord; 60 and 70 will produce discord; 60 and 65, worse discord. And so on. The science of musical composition lies in the management of sound-pulsation, and is governed by certain rigid mathematical laws—which laws the composer need not understand.
Air-movement may, of course, take place without sound-vibration, for air is only incidentally a sound-conductor. Earth, metal, water, and especially wood (along the grain), are better media than the atmosphere, for the transmission of sound. But sound may be transmitted without vibration of intervening sound-media. The electric current, passing along the telephone wire, picks up the sound waves at one end, and instantaneously deposits them, in good order and condition, at the other end—say, a couple of hundred miles away.
