2 



EXPLANATION OF SCIENTIFIC TERMS. 



the fissures of hard lavas. It melts 

 under the blowpipe into a semi-transpa- 

 rent glass. It is also called Cubizite. 

 See Vol. I., Polarization of Light, 

 p. 39. 



ANALYSIS is the separation of the parts 

 of a compound, so as to be able to examine 

 them apart. SYNTHESIS is the op- 

 posite, signifying the composition of parts 

 into one whole. 



ANAMORPHOSIS (Greek ana, again, and 

 morphosis, a form) is a distorted repre- 

 sentation of an object ; but which is so 

 made as to appear in its proper shape by 

 viewing it in a particular direction, or 

 through a particular medium. The figure 

 is also restored, in some cases, by causing 

 the anamorphosis to be reflected from 

 specula with certain surfaces, such as 

 those of cones and cylinders. 



ANGLE. See Gloss. I. 



ANGLES of Incidence, of Reflexion, and of 

 Draught. See Gloss. I. for these terms 

 respectively. 



ANHYDROUS. See Hydrate, Gloss. I. 



ANIMAL ELECTRICITY. See Galva- 

 nism. 



ANNEALING OF METALS consists in 

 making them red hot, and then letting 

 them cool gradually, in order to restore 

 their malleability, which they are apt to 

 lose under the operation of hammering. 

 The Annealing of glass is conducted in 

 the same manner, and is necessary to its 

 perfection ; for, otherwise, it would be 

 apt to fly into pieces by the slightest 

 scratch. See Rupert's dr"ps. 



ANTECEDENTS. See Ratio. 



APHELION is that point of the orbit of a 

 planet in which it is farthest from the 

 sun (Greek helios, the sun) ; and the 

 Perihelion is the point of the planet's near- 

 est approach. 



APLANATIC (Greek a privative, and 

 plane, error) signifies free from error. 

 The term is applied to those optical in- 

 struments in which the spherical aberra- 

 tion is completely corrected. See Aber- 

 ration, Spherical, in Gloss. I. 



APOGEE (Greek apo, from, and ge, the 

 earth) is that point of the moon's orbit in 

 which she is at the greatest distance ; and 

 the Perigee is that point in which she is 

 nearest to the earth. At the time when 

 the earth was regarded as the centre of 

 the system, the terms apogee and perigee 

 were applicable to the places of all the 

 planets, and also to the sun, with respect 

 to their variable distances from the earth ; 

 but now they refer only to the moon. 

 What was then called the sun's Apogee is 

 now the earth's Aphelion, and the Peri- 

 gee of the former has become the Peri- 

 helion of the latter. See Aphelion. 

 APOPHYLLITE,or FISH-EYE-STONE 

 is a scarce mineral, having a pearly lustre 

 like to the species of feldspar called 

 juoon-stone. Its crystals are various and 



often tessellated with thick tables irre- 

 gularly piled and grown together. It 

 has a white milky colour, but in its di- 

 vided portions it is usually transparent. 

 This mineral is found in the iron mines 

 of Uto, in Sudermania, a province of 

 Sweden. 



APPARENT TIME See Time. 



AQUA FORTIS. See Azote. 



AQUEOUS VAPOUR, the vapour of 

 water. See Vapour. 



ARC OF A CIRCLE. See Angle. 



AREA. The Roman area was a threshing 

 floor, but the word is used by geome- 

 tricians to denote any surface of a deter- 

 minate extent. This extent is ascertained 

 by calculating how many times larger the 

 surface is than that of another smaller 

 surface of the size of which we have an 

 idea, such as a square inch, a square foot, 

 &c., which we use as superficial measures. 



ARITHMETICAL PROGRESSION. 

 See Progression Arithmetical. 



ARRAGONITE, an impure species of car- 

 bonate of lime, brought from Arragon in 

 Spain. 



ARTIFICIAL MAGNETS. See Magnet. 



ASTRONOMICAL HORIZON. See 



' Horizon. 



ASYMPTOTES OF AN HYPERBOLA. 

 See Conic Sections in Gloss. I. 



ATMOSPHERE. See Gloss. I. 



ATMOSPHERES. One, two, three, &c. 

 See Gloss. I. 



REFRACTION OF. 



The atmosphere, which thus surrounds 

 the earth like a shell, is more dense than 

 the medium (whether ethereal or a vacu- 

 um) that intervenes between it and the 

 celestial bodies; and, consequently, the 

 rays of light are refracted when entering 

 this shell. This refraction varies with 

 the density of the atmosphere, and also 

 with the direction in which the rays 

 enter. The atmosphere gradually in- 

 creases in density from the higher to the 

 lower strata ; and, therefore, a ray of 

 light will be more and more refracted in 

 its passage to the earth's surface, so as to 

 descend in a curve line. The curve, too, 

 varies with the direction of the ray ; that 

 coming from the zenith alone being a 

 straight line. 



ATOM. See Molecule. 



ATTENUATION. See Alcohol. 



ATTRACTION IN GENERAL, CAPIL- 

 LARY, and of Cohesion. See Gloss. I. 



ELECTIVE. See Chemi- 

 cal Attraction. 



MAGNETIC. See Mag- 

 netism. 



AXINITE, a mineral commonly found in 

 crystals of four-sided prisms, so flattened 

 that some of its edges become thin and 

 sharp ; and hence its name from the 

 Greek axinc, an axe. 



AXIS OF AN ELLIPSIS, PARABO- 

 LA, or CONE, &c. See Gloss, I. 



