ANIMAL SOCXDS.] 



UNDULATORY FORCES ACOUSTICS. 



279 



pressing it down, midway between its two extremities, 

 Chen a shriller note will be produced, which will be an 

 octave higher than that afforded by the long cord. If. 

 again, a piece of steel be pressed against a rapidly 

 revolving tooth-wheel, a certain sound will be produced 

 but if the tooth-wheel be made to revolve twice as fast, 

 then the previous sound will be raised an octave. 



From these experiments we learn, that the tone of any 

 sound that is, its shrillness or dullness depends on the 

 number of vibrations produced in any similar period ol 

 time ; and that these, again, depend on the length of the 

 vibrating body the number of vibrations being inversely 

 as the length of the vibrating body. This will be more 

 easily understood if our readers will notice the length of 

 the different strings in a harp, or pianoforte. It will be 

 found, that those which produce shrill sounds, are 

 invariably the shortest ; and the deeper the sound, the 

 longer the string which produces the vibration. Violin 

 players are thus enabled to obtain any variety of the 

 sounds of other musical instruments, by means of the 

 rapid movement of their fingers over the strings ; for 

 they are enabled to shorten their lengths, so far as the 

 production of sound is concerned. 



We shall confine our illustration of these principles to 

 the eight notes in the treble clef forming an octave from 

 C below the lines, to C on the third space, as represented 

 below. To each of the notes we have appended their 

 names, for the assistance of those of our readers who do 

 not understand music. When, however, an instrument, 

 illy a pianoforte or harp, can be had access to, such 

 will materially aid in making our remarks understood. 

 Fig. 11. 





h names ... C 

 lu.im do do 



E 

 ml 



1 



f.i 



ABC 



la si da 



Now, the sounds of each of these letters, in Fig. 11, 

 are produced by a definite number of vibrations, and 

 the length of each string. Thus, that affording C 

 vibrates 240 times per second ; whilst the upper, or 

 octave C, will vibrate 480 times per second. The length 

 of the string producing the low C, may be 45 inches ; 

 whilst that producing the upper C, will be but 22; 

 inches. Each of the other notes will proceed from an 

 intermediate length of string and number of vibrations. 

 The following table gives the value of each of these com- 

 mencing with the lower C. Some consider that 256 

 vibmtinns equal C. We have chosen the lower number, 

 for the purpose of avoiding fractions ; but the reader can 

 easily calculate a table on that standard, by using the 

 table, or ratio, which follows this. 



Name of 

 note. 



C 

 D 

 E 

 F 

 G 

 A 

 B 

 



enffth of cord 

 in inches. 



45 

 40 

 36 

 331 



30 

 27 

 24 

 221 



Number of vibra- 

 tions per second. 



. 240 



. 270 



. 300 



. 320 



. 360 



. 400 



. 450 



. 480 



The law of the relation existing between the number 

 of vibrations, the length of the cord, and the nature of 

 the sounds produced, is thus at once made evident. 

 The ratio existing between each of these is shown in the 

 following table commencing with low C, as before, it 

 being the standard. 



Name of note ....CDEFG 

 Ratio of the length of \ . 



the cord . . . . / J * f 1 



Ratio of vibrations . 1 f {- -J J i ' ' 2 



From which we perceive, as before stated, that the 

 length of the cord is inversely as the number of 



B 



fV 



vibrations, and vice. vers3. We have already observed 

 that harmonies are afforded when certain sounds are 

 produced together. This occurs when C, and G (below), 

 which are five notes apart, C, and E (above), which are 

 three notes apart, and C, E, and G, are struck together 

 forming, as they do, a chord in which thirds and fifths 

 are combined. The effects of such combinations are 

 naturally pleasing to the ear : but this is not a pure 

 matter of taste only ; for if some pieces of paper are 

 allowed to fall on strings thus vibrating, they will 

 arrange themselves in such positions as will accord with 

 those of the length of the octave, the third, and fifth, 

 pointed out in our last table. We shall refer to this 

 again when speaking of acoustic figures. 



We have confined these remarks to stringed instru- 

 ments only ; but they are equally applicable to those in 

 which wind is alone employed. Thus, in the organ, the 

 length of the pipes corresponds to the length of the 

 string in the pianoforte, because they enclose a similar 

 length of air; and it is the vibration of this which 

 causes the sound of different notes. In the flute, 

 cornopean, etc., the length of the column of air is 

 regulated by the skill of the performer ; hence the diffi- 

 culty experienced in acquiring the art of blowing those 

 instruments properly. Many instruments, of entirely dif- 

 ferent kind of construction, such as the harmonium, 

 concertina, the pan-pipes, bells, <fcc., all owe the pro- 

 duction of their various notes to the laws we have here 

 explained. 



The diffusion of sound, from an instrument producing 

 it, is effected by means of a readily vibrating body. Of 

 such kind is the sounding-board of the piano, harp, 

 violin, <tc. We have already mentioned various facts re- 

 lating to this subject, and must therefore refer our readers 

 to our previous remarks.* Great variety exists in the 

 power, sweetness, and other qualities of instruments. 

 Thus the flute and the cornopean, although each pro- 

 ducing their sounds directly by the vibration of the air, 

 convey entirely different effects to the car. The same 

 may be said of the violin and harp, amongst stringed 

 instruments. These results chiefly arise from the nature 

 and quality of the material employed, and the skill 

 exhibited in their construction. A fastidious, or rather 

 educated musical ear, can detect great differences in this 

 respect ; and even to persons with no special musical 

 taste, it is by no means difficult to distinguish the tone 

 of the same kind of instruments made by different 

 manufacturers. It is, however, no part of our plan to 

 enter into such details ; our object being solely to illus- 

 ;rate the principles of which we have been speaking. 



Despite the perfection of many of the musical instru- 

 ments of our day, we still cannot arrive at the production 

 of that richness, body, and flexibility of tone which is 

 found in the human voice; and we shall now avail 

 ourselves of Dr. Bushnan's remarks in illustration of 

 that portion of our subject ; in which he also explains 

 the organs on which the sound-producing powers of 

 animals and birds depend. 



THE PRODUCTION OF ANIMAL SOUNDS. 



Organs of Voice and Speech in Man. The organs con- 

 cerned in voice and speech may be described as the chest 

 and lungs, the windpipe, the larynx, the posterior cavity 

 fit the mouth, the nostrils, which communicate with 

 that posterior cavity, the palate, the tongue, the teeth, 

 and the lips. The sounds wliich constitute voice, belong 

 to the order of musical sounds, independently altogether 

 of the singing voice. All that is rightly termed voice, 

 takes place in the larynx, which is properly the instru- 

 ment of voice. But even independently of the modifica- 

 tions by which voice is changed into articulate speech, 

 the voice is variously affected by the other parts which 

 have been enumerated : by the chest, as regulating the 

 force of the air; by the windpipe, as susceptible of 

 several degrees of length and tension ; by the posterior 

 cavity of the mouth, as offering an expanded vault ; by 

 the nostril, as affording a double passage of exit for tho 

 See ante, p. 275. 



