stica 



ACROI.KIM: 



say, in round number*, the ear receive* a musical impression from mny 

 ound whiuli arise* from a number of vibration* between 30 and 2000 ; 

 and we may certainly ay that, in every orchestra, the hearer* are 

 employed in ti-ting-'i'hing and discriminating between variou* rate* of 

 ucoeaoon in the undulation* of the air around them from 60 to 2000 

 per Moond, 



We hare previously alluded to a phenomenon of sound, or rather of 

 ciul>ind sounds, called a txal. If two note* whose vibration" nre 

 cither nearly in the name ratio, or nearly in one of the simple ratio* 

 above-mentioned, be *ounded together, the effect of their being out of 

 tune U a tremulou* motion of the Hound, the pulsation* or beat* of 

 which can be counted if the note* be not too high. For example, 

 up|KMc two >imulUneoiu note* whose vibration* are 100 and 104 per 

 woimt Here 25 vibrations) of the first are made during 26 of the 

 second ; and the reader who has studied the preceding jKirt of thin 

 article will nee that the resulting wave U as long an twenty-nix of the 

 ecood wave* ; but that if the wave* from the two be much alike in 

 their type*, thin resulting wave will consist of a cycle of rarefaction* 

 ami condensations very much resembling the separate wave*. The 

 whole reuniting wave being twenty-six times as long on the second 

 wave, will run through all its changes four time." in a second, which is 

 not sufficient to give a musical sound, but will only add to the sound of 

 one of the wave* the periodical tremulous sennation which is called a 

 beat, which may be imitated by ringing the syllables trim, ah, in rapid 

 succession on the same note of the voice. If, however, these bcat 

 recur at sufficiently short intervals to produce on the ear the imprc- 

 non of a continuous sound, a new note, called the graft harmonie, is 

 heard, lower than either separately. For information as to the use 

 made of these beat*, see the article TUIPEHAMKNT. 



It only remains to consider the different character of sounds. The 

 same note, a* to pilch or tone, may be sounded by a horn and a flute ; 

 nevertheless, each instrument has a character of its own, which 

 enable* every one to distinguish between the two. It is not to the 

 different loudneos of the two, for either, by skilful players, may be 

 made to give the weaker sound ; neither does it depend on the number 

 of vibrations, for that, as we have seen, determines only the pitch of 

 the note : the only difference between one wave and another of the 

 name length, is in the f'rrm of its type ; that is, in the different manner 

 in which the air is condensed and rarefied. There is also only this 

 feature left, to account for the difference between the tones which 

 different players will draw out of the same instrument; since both 

 Paganini and an itinerant street musician would make the same string 

 vibrate the same number of times in a second. Dr. Young examined the 

 string of a violin when in motion, and by throwing a beam of light upon 

 it and marking the motion of the bright spot which it made, he found 

 that the string rarely vibrated in the same plane, but that the middle 

 point would describe various and very complicated curves, corresponding 

 to different manners of drawing the bow. (' Lectures on Natural Philo- 

 ophy," voL ii. plate 5.) Professor WheaUtone has examined these curves 

 by the motion of a small bright bead on the end of a vibrating rod, 

 fixed vertically in a stand, and named by him a Kaltidophwe, and lias 

 calculated a large number of them on the principle of the *nj>fr-po*ition 

 of mall motwut, a principle which is the foundation of all the science 

 of vibratory motion, and may be thus enunciated : If the particles of 

 any body are acted on by several small forces, they will obey each, as 

 if it acted by iUelf ; and the motion of any particles in any direction 

 U the algebraic sum of the motion which would result from the dis- 

 turbing force* acting separately. 



We give three specimens of Young's figures, merely to show how 

 much the vibration produced by one player may differ that of another. 

 The waves proceeding from all three will be of the same length, the 

 vibration* being performed in the same time ; but the condensations 

 and rarefactions will evidently be such a* to give very different relative 

 tatm to contiguous particles of air. The middle of the stretched wire 



Fltr. 15. 



S&EZI ^HZ!5B\ 



describe* the curve on which it in placed, during what we have hitherto 

 called two vibrations. 



It might tend to throw light upon thin part of the subject if practical 



umxician* would observe, in the name manner, the curve* which 

 they produce, and describe the different qualities of tone arising 

 from them. A* yet, we have no direct experiment* which tend to 

 connect any particular form of vibration with any particular quality of 

 ound. We shall enter upon the best method of doing this in the 

 article CHORD. 



Some confusion arise* in books on this subject, from the use which 

 different author* make of the word* ribratiu* and mire. Some mean, 

 by a vibration, a motion to and fro, while others call the same motion 

 ''' vibration* ; and by a wave, the complete succession of condensation* 

 and rarefactions, which others call tiro waves, one of condensation, the 

 other "f rarefaction. For further information, we refer the reader to 

 Sir J. Herschel's article, already cited, to Robiaon's ' Mechanical I'lul.. 

 sophy.' liiot's I'm i-i KlemenUire de Physique/ and I'ouillet's ' Traits' 

 de Physique.' 



ACQUITTAL from the French arquittrr, to free or discharge, 

 signifies a deliverance or setting free of a person from a charge of guilt. 

 One who, upon his trial for a criminal offence, is discharged by the 

 jury, is said to be acquitted. The acquittal by the jury ban, how, \ ,-r. 

 no force in law until judgment has been given upon the verdict by the 

 court. After this judgment, if the party be indicted a second time fur 

 the game offence, he may plead hia former acquittal in bar, as a com- 

 plete answer to the second charge, by what is called a plea of Mfn/i'. 

 Hfijuit. Upon this plea being admitted or proved, the person indicted 

 will be entitled to be discharged, as the law will not permit a m.m to 

 be twice put in danger of punishment for the same offence. 



ACQUITTANCE is a discharge in writing of a debt. or MIIU of 

 money due. A general receipt or acquittance in full of all demands 

 will discharge all debts, except such as are secured by what are termed 

 specialties, viz. bonds and ingtrumenU under seal, which are con- 

 sidered by the law u of too great force to be discharged by a verbal 

 concord and agreement, or any less formal and solemn acquit t-izicc th.m 

 a deed. Where an' acknowledgment of satisfaction is by deed, it may 

 operate as a good answer to an action on the debt. CM-M tlr.u <U nothing 

 has ever been actually received. 



Courts of equity, and even courts of law in some eases, will m.l.-i 

 accounts to be gone into anew, notwithstanding the production ! a 

 general acquittance or receipt in full of all demands, upon proof that 

 Mich acquittance wa obtained by fraud or given under a mistake. ..n.l 

 that the debt or other demand has not been in fact satisfied. 



ACRE, a measure of land, of different value in the different parts of 

 the United Kingdom. When mentioned generally, the statute or 

 English acre is to be understood. Its magnitude may be best i . 

 to that of the square yard by recollecting that a square whose side i- 

 22 yards long U the truth part of an acre; whence the latter contains 

 '2'2 x '2'2 x 10, or 4840 square yards. The chain with which land is 

 measured is 22 yards long ; so that lm square chains are on< 

 This measure is divided into 4 roods, each rood into 40 perches. *>. tint 

 each perch contains 30J square yards. Thus : 



Acre, 



Hood. 



Perch. 



4 - 160 



1 = 40 



1 



Square Side of cquh ult-nt 



;:ml-. Mjaarn in > .oil . 



4840 69-57H1 



1210 34-7851 



an; 



5-5 



The Irish acre is larger than the English, inasmuch as 1 00 Irish acre* 

 are very nearly equivalent to 162 English acres. More correctly, l!il 

 Irish acres are 1M6 English acres ; but the former ratio point* out an 

 easier arithmetical operation, ami will not !x> wrong by so much as one 

 acre out of 5000. 



The Scottixh acre is also larger than the English, 48 Scottish acres 

 being equal to 61 English acres. There are also local acres in various 

 parts of England, such as the Cheshire acre of 8 yards to the pole. The 

 English statute acre U u-vd in the United States of North Am. , 



The French Art in* square whose side is 10 metres, and 1000 Eng- 

 lish acres ore equivalent to 40,466 ares. 



ACROLEINE (C.H.O.), a substance obtained by the dehydration of 

 glycerine (C.H.O. = C,H 0, + 4HO), and by the oxidation of allylic 

 alcohol (C.H.O, + p, = C H.O t + 2HO). It was obtained by Redten- 

 bacher by the distillation of glycerine with phosphoric acid. The 

 operation must be carried on in vessels charged with carbonic acid i;.i, 

 as acroleine is rapidly oxidised in atmospheric air. It may be regarded 

 as the hydride of a radical called arryl. This substance resembles 

 aoetyl, or othyl, and represents in acroleine the position of aectyl in 

 acetic aldehyde. Thus, H,C ? H,0, is the atomic constitution of acro- 

 leine. which when oxidised in the atmosphere becomes converted into 

 Arrylir acid. HO, C e H,O,, a substance perfectly analogous to acetic 

 acid. Acroleine is often formed on a result of the distillation ..f ,.;]- 

 and fat*. Thus, castor-oil yields acroleine and Rome other peculiar 

 products on distillation. 



Acroleine is a limpid colourless liquid. Its vapours are intolerably 

 pungent and suffocating (whence its name), attacking the eyes and 

 respiratory organs moat violently ; a very minute quantity will produce 

 this effect. The unpleasant, pungent smell of a blown-out candle when 

 the wick is loft in a state of ignition is due to a trace of this subst-.m < . 

 Its sp. g. is loss than that of water ; it boils at 12. r >, and is soluble in 

 40 parts of wafc-r. Even in sealed vessels it cannot be long preserved, 

 becoming converted cither into a white, flocculent, inodorous powder 



