GNO 



GNO 



GNETUM, in botany, a genus of the 

 Monoecia Monadelphia class and order. 

 Natural order of Piperitac. Urticae, Jus- 

 sieu. Essential character : male an ament 

 with scales ; corolla none ; filaments one, 

 with two anthers : female an ament with 

 scales; corolla none ; style with a bifid 

 stigma; drupe with one seed. There is 

 only one species, vi:. G. gnemon, a native 

 of the East Indies, where the leaves, male 

 catkins and fruits, are eaten. 



GNIDIA, in botany, a genus of the 

 Octandria Monogynia class and order. 

 Natural order of Vepreculae. Thymeleae, 

 Jussieu. Essential character : calyx fun- 

 nel-form, four-cleft ; petals four, inserted 

 into the calyx ; seed one, somewhat ber- 

 ried. There are eleven species. 



GNOMON, in dialing, the style, pin, or 

 cock of a dial ; which, by its shadow, 

 shows the hour of the day. The gno- 

 mon of every dial represents the axis 

 of the world. See DIAL and Di AUNG. 



GXOMON, in geometry. If, in a paral- 

 lelogram (PI. VI. Miscel. fig. 1.) the dia- 

 meter A C, be drawn ; also two lines, 

 E F, H I, parallel to the sides of the pa- 

 rallelogram, and cutting the diameter in 

 one and the same point, G, so that the 

 parallelogram is, by these parallels, divi- 

 ded into four parallelograms, then are 

 the two parallelograms, D G, B G, through 

 which the diameter does not pass, called 

 complements ; those through which the 

 diameters pass, E H, F I, are called the 

 parallelograms about the diameter; and a 

 gnomon consists of the two complements, 

 and either of the parallelograms about 

 the diameter, viz. G D -|- H E -f E I, or 

 GD-r-FIH-GB. 



GWOMON, in astronomy, a stile erected 

 perpendicular to the horizon, in order to 

 find the altitude of the sun. Thus in the 

 right angled triangled ABC, fig. 2, are 

 given A B, the length of the stile, B C, 

 the length of its shadow, and the right 

 angle, ABC. Hence, making C B, the 

 radius, we have this analogy for finding 

 the angle, A C B, the sun's altitude, viz. 

 BC: A B : : radius: tangent of the angle C. 



By means of a gnomon, the sun's meri- 

 dian altitude, and consequently the lati- 

 tude of the place, may be found more ex- 

 actly than with the smaller quadrants. 



By the same instrument, the height of 

 any object, G H, may be found ; for as 

 D F, fig. 3, the distance of the observer's 

 eye from the gnomon is to D E, the height 

 of the stile, so is F H, the distance of the 

 observer's eye from the object, to G H, 

 its height. 



the Gnomon may be made useful in 

 taking the meridian altitude of the sun, 

 and thence finding the latitude of the 

 place. Having a meridian line drawn 

 through the centre of the gnomon, mark 

 the point where the shadow of the gno- 

 mon terminates when projected along 

 the meridian line, and measure the dis- 

 tance of that point from the centre of 

 the gnomon, which will be the length of 

 its shadow ; then, having the height of 

 the gnomon, and the length of the sha- 

 dow, the sun's altitude is easily found. 

 Thus, if A B be the gnomon, and A C 

 the length of the shadow, then in the 

 right angled triangle, A B C, we have 

 A B and B C given ; hence the angle C 

 is easily found, for C B : B A : : radius : 

 tangent of the angle C ; that is, as the 

 length of the shadow is to the height of 

 the gnomon, so is radius to the tangent 

 of the sun's altitude above the horizon. 

 Ex. We learn from Pliny, at the time of 

 the equinoxes, that the shadow was to 

 the gnomon as 8 : 9, therefore we say as 

 8 : 9: :R : |=1.125, the tangent of an an- 

 gle of 48 22', which is the height of the 

 equator at Rome, and its complement 

 41 38' is therefore the height of the 

 pole, or the latitude of the place. This 

 method, however, requires correction for 

 the sun's parallax, and for refraction. 



GNOMONICS, the art of DIALING, 

 which see. From the shadow of a rod, 

 perpendicularly or obliquely placed on a 

 plane, may be determined a triangle, by 

 drawing from the top of the rod a line 

 that shall touch the luminous body, form- 

 ing with the rod the least possible angle. 

 The sides of the triangle will be, first, 

 the part of this line comprehended be- 

 tween the top of the rod and the given 

 plane ; then the rod itself; and lastly, the 

 line drawn from the bottom of the rod 

 till it meets the other line already men- 

 tioned. This last line will be the shadow 

 relatively to the given plane : it will in- 

 crease and decrease in proportion as the 

 sine of the angle, whose summitcoincides 

 with the summit of the rod, shall be 

 greater or less, that is, in proportion as 

 the luminous body shall descend or as- 

 cend with respect to the given plane ; 

 and if that body move to the right or the 

 left of the position first occupied by the 

 triangle, that determines the shadow, 

 which will move on the plane in a con- 

 trary direction ; and on these principles 

 the art of dialing consists. 



GNOSTICS, in church history, a sect 

 of Christians, so called from their preteiv 



