ARl 



ARS 



admit it, in conformity to his principles 

 of reasoning, or in consistency with his 

 own conduct, situation," &c. 



1. The argumentum ad hominem, in 

 the popular but less scientific sense, " is 

 addressed to the peculiar circumstances, 

 character, avowed opinions, or past con- 

 duct of the individual, and therefore has 

 a reference to him only, and does not 

 bear directly and absolutely on the real 

 question, as the argumentum ad rem does. 



2. "The argumentum ad verecundiam, 

 in like manner, is described as an appeal 

 to our reverence to some respected au- 

 thority, some venerable institution, &c. ; 

 and the argumentum ad populum, as an 

 appeal to the prejudices, passions, &c., of 

 the multitude. 



3. "The argumentum ad ignorantiam 

 is usually enumerated with these, but is 

 evidently nothing more than the employ- 

 ment of some kind of fallacy, in the 

 widest sense of that word, towards such 

 as are likely to be deceived by it." 



A'RIES. A zodiacal constellation of 

 lixed stars, drawn on the globe in the 

 figure of a ram. It is the first of the 

 twelve signs of the zodiac, from which a 

 twelfth part of the ecliptic takes its 

 name. It indicates the first month of 

 autumn, extending from the 20th of Sep- 

 tember to the 20th of October. It con- 

 sists of Q6 stars. 



A'RIETIS. A star of the second 

 magnitude, in the head of the Ram. 



ARI'LLUS. A terra applied, in Bo- 

 tany, to an expansion of the placenta, or 

 funiculus, about the seed : the mace of 

 the nutmeg, and the red covering of the 

 seed of the spindle-tree, are in^tances. 



ARI'STOLOCHIA'CE^ {ikpiaroi, the 

 best, Aoxem, delivery). The Birthwort 

 tribe of Dicotyledonous plants, so named 

 from the reputed emmenagogue proper- 

 ties of the genus Aristolochia. Herba- 

 ceous plants or shrubs, with leaves alter- 

 nate; flowers apetalous, hermaphrodite; 

 stamens epigynous ; ovary many-celled; 

 fruit dry or succulent, many-celled. 



ARI'THMETIC ('dpieiJ^o^, number). 

 The science which treats of numbers, of 

 the mode of expressing them, of the 

 manner of computing by them, and of 

 the various uses to which they are ap- 

 plied in the practical business of life. 



1. Arithmetical Complement. That 

 which a number wants of the next high- 

 est decimal denomination. Thus, what 

 7 wants of 10, viz. 3; what 32 wants of 

 100, viz. 68; what 159 wants of 1000, 

 viz. 841 ; or .017 of 1, viz. .983 ; are the 



arithmetical complements of these num- 

 bers. 



2. Arithmetical Mean. That number 

 or fraction which is intermediate between 

 two other numbers, as 10 between 6 and 

 14; 10^ between 4 and 17. To find the 

 arithmetical mean, take the half sum of 

 the two numbers. 



A'RMATURE {armatura, armour). A 

 term, in its general sense, denoting 

 armour. A natural magnet is, however, 

 said to have an armature, or to be armed, 

 when its two poles are polished and 

 covered over with smooth plates of iron, 

 which terminate in two strong projecting 

 ends. The magnetic power, imparted by 

 this means to the two iron plates, is con- 

 centrated in the knobs, and thus a north 

 and a south pole are made. 



A'RMILLARY SPHERE {armilla, a 

 bracelet). A hollow sphere, representing 

 the several circles of the globe : it is so 

 constructed that all the surface of the 

 sphere is cut away, except the equator, 

 ecliptic, colures, &c. See Astrolabe. 



A'RQUIFOUX. A lead ore, commonly 

 called potters^ ore, from its being used by 

 potters as a green varnish. 



A'RRAGONITE. An impure species 

 of carbonate of lime, found in Arragon 

 in Spain. It occurs in the form of fibrous 

 branches, which ramify from a centre, 

 called flos ferri, or iron-flower. 



ARROW-HEADED CHARACTERS. 

 A term applied to certain marks stamped 

 on the bricks of Babylon, and cut on the 

 marble monuments at Persepolis. Their 

 character is formed from the isosceles tri- 

 angle or wedge, and hence they are termed 

 in liatin cuneiformes, or wedge-shaped. 



A'RSENIC {apaeviKov, masculine; an 

 old epithet, denoting powerful properties). 

 A bluish-white metal, of great brilliancy, 

 resembling steel. The arsenic of com- 

 merce, commonly called white arsenic, 

 and known as a violent poison, is arse- 

 nious acid. The fuming liquor of arsenic 

 is the sesquichloride, a colourless volatile 

 fluid, which fumes strongly on exposure 

 to the air. Realgar, also called ruby, or 

 red arsenic, is the protosulphnret. Orpi- 

 ment, or yellow arsenic, is the sesquisul- 

 phuret, and constitutes the colouring 

 principle of the pigment called king's 

 yellow. Another well-known pigment, 

 called Scheele's mineral green, consists of 

 an arsenite of copper. On exposing the 

 metal to a moist atmosphere, a black 

 powder is obtained, called poudre a 

 mouches, or fly-powder. Lastly, a solu- 

 tion of arsenic in muriatic acid, heated 



