ACT 



affctflions of the mind, auj voluntary motion ; which arc not 

 abfoluttly luccflar)- to the life of the animal, but conducive 

 to its comfortable exillei.ce. 



In the year 1752, Dr. ^Vhite publifhcd an ingenious 

 performance, under the title of an Efiay on the vital and 

 other voluntary Motions of Animals, 8vo. ; and in the fame 

 year Dr. Simpfon alfo publilhtd a book on X'ital and Ani- 

 mal Anions, 8vo. 



j\cTiON, in Mechanics, denotes cither the effort which 

 one body or power exerts againll another, or the cffctt re- 

 fultlng from fuch effort : or more accurately, the motwn 

 which a body really produces, or tends to produce, in an- 

 otlicr. The aftion of a body becomes apparent only by 

 its motion ; and we cannot affix any prccife idea to the 

 term action than that either of adtual motion, or a iimple 

 tendency to motion. 1-eibnitz and his difciples.for want of 

 dulv attending to the proper and difcriminating idea ot the 

 word aftion, have perplexed themfelves and others with up- 

 profitable and indecifive difputes coixerning vis vivn, and 

 vis mortua. Kee FoRCt. 



The Cartefians refolve all phyfical aftion into metaphyli- 

 cal. According to them, bodies do not acl upon one an- 

 other ; but the action proceeds immediately from the Deity: 

 the motions of bodies, which fecm to be the caufe, being- 

 only the occafions of it. See Qccaficncl cause. Action is 

 either inilantancous or continued ; that is, either by per.*-. 

 culHon, or by preffure. Thefe two forts ol aihlion are hetero- 

 geneous quantities, and are not capable of mutual compa- 

 rifon any more than a line can be compared v.ith a furface, 

 or a furface with a folid. The leall degree of percuiTion 

 mav be made to overcome the preffure of the greateil 

 weight. Thefe aftions, therefore, cannot be nieafured one 

 by the other ; but each of them muft liave a meafure of its 

 own kind, as fohds are meafured by iolids, and iurfaces by 

 farfaces ; becaufe time is concerned in the one, but not in 

 the other. 



It is one of the laws of nature, that aftion and re-aftion, 

 are always equal, and contrary to each other. 



If a body be urged by equal and contrary aftions, it will 

 remain at reft. But if one of thefe aftions be greater than 

 its oppofite, motion will enfue towards the parts lead 

 urged. 



it is to be obferved, that the aftions of bodies on each 

 other, in a fpace that is carried uniformly forward, are the 

 fame as if the fpace were at reft ; and any powers or forces 

 that aft upon all bodies, fo as to produce equal velocities in 

 them in the fame, or in parallel right lines, have no effedl 

 on the mutual actions, or relative motions. Thus the mo- 

 tions of bodies on board a fhip, that ij earned fteadily and 

 uniformly forward, are performed in tlie fame manner as if 

 the fhip were at reft. The motion of the earth round its 

 axis has no effect on the aftions of bodies and agents at its 

 fui-face, except fo far as it is not uniform and reftilincal. 

 In general, the aftions of bodies upon each other depend 

 not upon their absolute, but ielative motion. 



For the adlions of powers, fee Friction, Force, Me- 

 chanics, Motion, Power, and Resistance. For the 

 laws of the aftlon of fluids, &c. fee Fluid, and Specific 

 Gravity. 



Action, quantity of, in Mechanics, an espreffion ufed by 

 M. de Maupertuis, in the Mem. of the Acad, of Sciences 

 of Paris for 1744, and in thofe of Berlin, for 1746, to de- 

 note the continual produft of the mafs of a body, by the 

 fpace through which it runs, and by its celerity. He lays 

 it down as a general principle, that, " whenever any changes 

 happen in nature, the quantity of aftion neceffaiyto produce 

 this change is always the leaft. pofTjbk." And this, h? lays. 



ACT 



is a law indicating the higheft wifdom. This principle he 

 applies to the inveftigation of the Jaws of refraction, the 

 laws of the collifion of liard and elaftic bodies, and even the 

 laws of reft, as he calls them, that is of the equilibrium or 

 equipollency of prefTuivs ; aiid, thus inveftigating the laws 

 of motion, referring thefe and the laws ol equilibrium to the 

 fame p.-inciple, and connecling the metaphyfical confidei-a- 

 tion of iinj caufes with thi^ fundamental doflrines of me- 

 chanics, he deduces what he conceives to be a ftronger 

 proof of the exiftcncc of a Deity, or of a firft intelligent 

 caufe, than the other argumenttocommoaly alledged, and 

 derived from the oit^BI" of nature. 



It may be obfer^jed, however, that the quantity of ailion, 

 according to the definition of M. de Maupertuis, is in 

 reality the fame with the produft of the mafs into the 

 fquarc of the celerity, when the fpace palled over is equal 

 to that by which the celerity is meafured ; and therefore 

 the force or quantity of m.otion will be proportional to the 

 mafs multiplied by the fquare of the velocity ; fince the 

 fpace is ir.eafiu'^ by the \elocity continued for a certain 

 time. 



In the fame year that Maupertuis communicated his 

 principle, ProfefTor Euler alfo demonftrated, in the fupple- 

 meiit to a trcatife intitled Trietboclus inveiiiendi Lineas curvas 

 maximi I'el minimi proprietate gaudentes ; that in the tra- 

 jeftories defcribed by bodies urged by central forces, the ve- 

 locity multiphed by what the foreign mathematicians call 

 the element of the curve, is always a >;:iii:mitm ; which 

 Maupertuis confidered as an application of his principle to 

 the motion of the planets. For the manner in which this 

 principle of a minimum may be deduced from the Newtonian 

 theoiy of refraction ; fee Refraction. 



Action, in Ethics, or moral Action, is a voluntary 

 motion of a creature capable of diflinguiihing good and 

 evil ; whofe effecft, therefore, may be juftly imputed to 

 the agent. 



A mo)-al aBion may be more fully defined to be whatever 

 a man, confidered as endued with the powers of underftand- 

 ing and willing, with refpe£l to the end he ought to aim at, 

 and the rule he is to regard in acting, refolves, thinks, does, 

 or even omits to do ; in fuch a manner as to become ac- 

 countable vfor v>hat is thus done or omitted, and the confe- 

 quences thereof. 



In the ftrict philofophical fenfc, fays Dr. Reid (Effays on 

 the Active Powers of Man, p. 97) nothing can be called 

 the attion of a man, but what he pievioully conceived, and 

 willed or determined to do. In morals the word is com- 

 monly employed in this fenfe, nor is any thing imputed to- 

 a man as his doing, in which his will was not interpofed. 



The foundation, then, of the morality of aftions is, that 

 they are done knowingly and voluntarily : and all morai 

 aftions may be divided, with refpeft to the rule, into good 

 and evil. 



But when moral imputation is not concerned, many things 

 are called the aftions of a man, which he previoufly neither 

 conceived nor willed. Hence the aftions of men have been 

 diftinguiflied into three clafTes, the voluntary, the involun- 

 tary, and the mixed. By the laft are meant fuch aftions as- 

 are under the command of the will, but are commonly per- 

 formed without any intei-pofition of the will. See Active 

 Poiuer, Motive, Principles of ylclioa. and Virtue. 



Action, in Oratory, is an accommodation of the perfon 

 of the orator to his fubjeft ; or, a management of the coun- 

 tenance, voice, and gelture, fuited to the matter fpoken or 

 delivered. 



Aftion makes one of the greateft branches or divifions of 

 rhetoric. The ancients ufually call it pronunciation. 



AftioH 



