FIF 



gen, metallic iron, and hydrogen ; also 

 called ferruretted chyazic acid. It con- 

 tains the elements of hydro-cyanic acid, 

 but differs from it totally in its properties. 

 Its salts, formerly called triple prussiates, 

 are now termed ferro-cyanides. The 

 beautiful pigment Prussian blue is a 

 ferro-cyaiiide of the peroxide of iron. 



FERRU'GINOUS [ferrugo, quasi ferri 

 CBrugn, rust of iron). Containing iron, 

 or of the nature of iron, as certain salts, 

 mineral waters, &c. The term ferrugo 

 is applied, in Botany, to a disease of 

 plants, commonly called rust, and occa- 

 sioned by the presence of minute fungi, 

 chiefly of the genus uredo. 



FERTILIZATION {fertilis, fertile). 

 The function of the pollen of plants upon 

 the pistil, by means of which the ovules 

 are converted into seeds. 



FETTSTEIN (German, fat stone). A 

 designation of a sub-species of pyramidal 

 felspar, from its resinous nature. The 

 term is synonymous with elaolite, which 

 means oil-stone. 



FIBRE {fibra, a filament). A filament 

 of thread, of animal, vegetable, or mineral 

 composition. A fibril is a minute sub- 

 division of a fibrous root. 



FI'BRIN {fibra, a fibre). A principle 

 found in vegetables as a constituent of 

 gluten ; and in the living blood of ani- 

 mals, constituting muscular fibre. 



FrBROLITE. A mineral of a pecu- 

 liar fibrous texture, found in the Car- 

 natic, and consisting of alumina, silica, 

 and iron. 



FIBROUS {fibra, a fibre or thread). 

 Consisting of or resembling fibres ; as 

 indicating the structure of a shell when 

 fractured. 



FI'BROUS COAL. A variety of 

 glance-coal, distinguished by its fibrous 

 concretions and silky lustre. It occurs 

 in the coal-fields of Great Britain. 



FIELD OF VISION. A technical 

 expression for the space or range seen 

 through a telescope. It is measured by 

 dividing the angle under which it is seen 

 by the angle of vision of the naked eye 

 embracing the same field within its view. 

 The greater the magnifying power of the 

 instrument, the less will be the angle of 

 vision of the naked eye, compared with 

 that of an eye looking through the 

 glass. 



FIFTH. An interval in Music, occur- 

 ring in the natural scale, in the fifth 

 place from the fundamental. The false 

 fifth is less than the fifth by a lesser 

 semitone. 

 136 



FIG 



FIFTEENTH. In Music, an interval 

 of two octaves. The fifteenth stop in 

 organs is a double octave above the dia- 

 pason. 



FI'GURATE NUMBERS. Certain 

 series of numbers deduced from any pro- 

 gression, by taking the sum of the first 

 two, the first three, the first four, &c., 

 terms of the progression, and then ope- 

 rating on the series thus obtained, in 

 order to obtain a new series, and so on. 

 For example : — 



A 1, 2, 3, 4, 5, 6, 7, 



B 1, 3, 6, 10, 15, 21, 28, 



C I, 4, 10, 20, 35, 56, 84, 



D 1, 5, 15, 35, 70, 126, 210. 



1. The series A is the arithmetical 

 progression from which the other series 

 are deduced. The series B consists of 

 triangular or polygonal numbers of the 

 preceding progression, so named from 

 certain analogies which the numbers so 

 denoted have with the geometrical figures 

 bearing the same denominations. The 

 series C consists of triangular pyramidal 

 numbers, and is formed from the pre- 

 ceding series in the same way as this 

 from the original progression. The series 

 D consists of second pyramidals, and is 

 formed like the preceding series. 



2. If the common difference of the first 

 progression were 2, the successive series 

 would consist of square numbers ; if the 

 common difference were 3, the series 

 would be pentagonal numbers ; if 4, 

 hexagonal numbers, and so on; the num- 

 bers thus obtained being capable of being 

 placed in the form of squares, pentagons, 

 hexagons, &c. 



FIGURE. Figure, or form, is a pro- 

 perty of bodies, resulting from extension. 

 The volume of a body has no relation to 

 its figure: bodies which have the same 

 figures may possess very different vo- 

 lumes; and bodies may have the same 

 volume under very different figures; 

 thus, two masses of matter may present 

 the same volume, although the one be 

 round and the other square. 



FIGURE (in Geometry). A finite 

 space, bounded on all sides by lines or by 

 planes. The term is also employed as 

 synonymous with diagram. 



FIGURE, APPARENT. A term in 

 Optics, denoting the figure under which 

 an object presents itself to the eye. As 

 this depends on the situation of the 

 points from which the rays of light pass 

 to the eye, the apparent figure may be 

 very different from the real figure of an 

 object ; a straight line, for instance, may 



