ACIRS ACOUSTICS, 



23 



for the alkaline, earthy, and metallic oxyds, with 

 which they form neutral salts. Some acids liave no 

 sour taste, but their affinity for the three classes of 

 bodies above-mentioned is always characteristic. If 

 a few drops of sulphuric acid, nitric acid, or muriatic 

 acid, be added to a solution of blue litmus, it becomes 

 red. The same is the case if they be added to other 

 vegetable colours, as violet, &c. Hence these colours 

 are employed as tests of acids, that is, to ascertain 

 when they exist in any substance. We may add the 

 infusion to the fluid in which we are trying to detect 

 mi acid, but a more convenient method is, to spread 

 it on paper, and allow it to dry. If a strip of this be 

 put into a fluid in which there is an acid, it instantly 

 becomes red. Some acids appear only in a fluid state, 

 <-idier gaseous, as carbonic acid, or liquid, as sul- 

 phuric acid ; others appear in a solid form, or crys- 

 talized, as benzoic acid, boracic acid, &c. All acids 

 are compound bodies, and are sometimes divided into 

 four classes, the three first of which are compounded 

 with oxygen ; the fourth class consists of those 

 which, at least according to those modern chemists, 

 Jiave no oxygen ; e. g. sulphuretted hydrogen. 

 The first class consists of acids compounded with 

 oxygen and one other body ; the second class com- 

 prises the acids compounded of carbon, hydrogen 

 and oxygen; and the third class consists of those 

 acids which contain nitrogen, in addition to the 

 three substances above-mentioned. The ancient 

 chemists were acquainted with but few of the acids 

 now known; they divided them, according to the 

 kingdoms of nature, into mineral, vegetable, and 

 animal acids. This division, however, cannot now 

 be retained, as there are some acids which appear in 

 all the kingdoms ; e. g. phosphoric acid. If thesame 

 radical be compounded with different proportions of 

 the acidifying principle, forming different acids, the 

 most powerful acid receives a name from the radical, 

 terminating in -ic ; the .weaker, a name formed in 

 the same manner, in -ous ; e. g. sulphurous acid and 

 sulphuric acid, nitrous and nitric acid; and, where 

 there are intermediate compounds, the term hypo is 

 occasionally added to the compound next above it in 

 point of acidity. Thus hyposulphuric acid signifies 

 an intermediate acid between sulphurous and sul- 

 phuric acids ; hypophosphorous acid, an acid containing 

 less oxygen than the phosphorous acid. ( For Prussic 

 acid, Pyroligneous acid, c., see Prussic, Pyroligne- 

 ous.) 



ACIRS ; hurricanes of snow which^fjrevail ;urioii<y 

 the Cevennes, in the south of France. Village-- are 

 sometimes so rapidly covered, that the inhabitants 

 have no means of communication, but by cutting pas- 

 sages under the snow. 



ACOLYTHI, or ACOLYTES; servants of the church, 

 who appeared in the Latin church as early as the 3d 

 century ; but in the Greek 1 , not till the 5th. Their 

 office was to light the candles, thence they were 

 called accensores ; to carry the tapers to the festal 

 processions, thence ceroferarii ; to present the wine 

 and water at the supper ; and, in general, to assist 

 the bishops and prie sti in the performance of the 

 ceremonies. They belonged to the clergy, and had 

 ;. rank immediately below the subdeacons. In the 

 Roman church, the consecration of an acolythus is 

 the highest of the lower kind of ordination. The 

 person ordained receives a candlestick and chalice, 

 in token of his ancient employment. The duties, 

 however, formerly appertaining to this office, have 

 been performed since the 7th century by menials and 

 boys taken from the laity, who are improperly called 

 acolythi, in the books of the liturgy of the Catholic 

 church. The modern Greek church no longer re- 

 tains even the name. r 



ACONITA; a vegetable poison, recently extracted 



from aconitum napelhts, or wolf's-bane, (properly 

 alkaline,) by Mr Brande. The analysis has not yet 

 been made known. 



ACONZIO, or ACONTIUS, James, a philosopher, 

 mathematician, and divine of the 16th century. He 

 was a native of Trent, and died about 1505. His 

 principal works are one Km the Stratagems of Satan, 

 md another on the Method of Studying the Sciences, 

 In these he displays^ liberality and foresight beyond 

 the spirit of his age. * 



ACOSTA, Uriel, a Portuguese, of the 17th century, 

 who from Christian turned Jew, and from Jew un- 

 believer ; and in consequence underwent numberless 

 persecutions. He died by his own hand in 1640 ; and 

 his life, an interesting account of which has been 

 often published, furnishes a notable example of into- 

 lerance and bigotry on one side, and the inutility of 

 pursuing certain lines of inquiry without steady prin- 

 ciples, and a calm temperament on the other. 



ACOUSTICS. One of our most important connexions 

 with external objects is maintained through the 

 sense of hearing ; that is, by an afl'ection which cer- 

 tain actions or motions, in those objects, produce on 

 the mind, by being communicated to it through the 

 ear. The peculiar excitation or motion perceptible 

 by the ear is called sound ; and the consideration of 

 this motion, its qualities and transmissions, forms the 

 science of acoustics. Philosophers make a distinction 

 between sound and noise : thus those actions which 

 are confined to a single shock upon the ear, or a set 

 of actions circumscribed within such limits as not to 

 produce a continued sensation, are called a noise; 

 while a succession of actions which produce a con- 

 tinued sensation -are called a sound. It is evident 

 from the mechanism of the ear, so far as it is under- 

 stood, that it is a refined contrivance for conveying a 

 motion from the medium which surrounds it to the 

 auditory nerve ; and that this nerve must receive 

 every motion excited in the tympanum. Every 

 motion thus excited, however, does not produce the 

 sensation of sound. That motions may be audible, 

 it is necessary that they impress themselves upon the 

 medium which surrounds the ear with velocities com- 

 prised within certain limits. These motions are com- 

 monly produced by disturbing the equilibrium which 

 exists between the parts of a body. Thus, for ex- 

 ample, if we 'strike a bell, the part which receives 

 the first impulse of the blow is driven nearer to the 

 surrounding parts ; but the impulse having ceased, 

 it is urged oack by a force of repulsion which exists 

 in .the metal, and made to pass beyond its former 

 position By the operation of another property of 

 the metal, namely, cohesive attraction, it is then 

 made to return in the direction of its first motion, 

 again, beyond its position of repose. Each of these 

 agitations influences the adjacent parts, which, in 

 turn, influence those beyond them, until the whole 

 mass assumes a tremulous motion ; that is, certain 

 parts approach to and recede from each other ; and it 

 only recovers its former state of repose, after having 

 performed a number of these sonorous vibrations. 

 It is evident that such vibrations as are here de- 

 scribed must result from the combined operation 

 of attraction and repulsion, which, together, con- 

 stitute the elasticity of solid bodies. When fluids, 

 whose elasticity is confined to repulsion, emit sounds, 

 a force equivalent to that of attraction in solids is 

 supplied to them by external pressure. The so- 

 norous vibrations of bodies, are exceedingly curious, 

 and the more difficult to be understood from our 

 habits of measuring changes or motions by the sight ; 

 but these motions affect very sensibly another organ, 

 while they are almost imperceptible to the eye ; and, 

 as we are without the means of converting the ideas 

 derived from one sense into those derived from 



