ODE 



OEN 



be inscribed in a circle. If the radius of a 

 circle, circumscribing a regular octagon, 

 be = r, and the side of the octagon = y, 



then y = </2^ r ^/2r*. 



OCTAGON, in fortification, denotes a 

 place that has eight bastions. 



OCTAHEDRON, or OCTAEDRON, in 

 geometry, one of the five regular bodies, 

 consisting of eight equal and equilateral 

 triangles. Seethe article BODY. The 

 square of the side of the octahedron is 

 to the square of the diameter of the cir- 

 cumscribing sphere, as 1 to 2. If the 

 diameter of the sphere be 2, the solidi- 

 ty of the octahedron inscribed in it will 

 be 1.33333, nearly. The octahedron is 

 two pyramids put together at their bases, 

 therefore its solidity may be found by 

 multiplying the quadrangular base of 

 either of them, by one-third of the perpen- 

 dicular height of one of them, and then 

 doubling the product. 



OCTANDRIA, in botany, the eighth 

 class in Linnzeus's system, Consisting of 

 plants with hermaphrodite flowers, which 

 are furnished with eight stamina or male 

 organs of generation. There are four or- 

 ders belonging to this class of plants, 

 which derive their names from the num- 

 ber of female organs possessed by the 

 plants of each respective division. 



OCTANT, or Oclik, in astronomy, that 

 aspect of two planets, wherein they are 

 distant an eighth part of a circle, or 45 

 from each other. 



OCTAVE, in music, an harmonical in- 

 terval, consisting of seven degrees, or les- 

 ser intervals. See Music. 



OCTOBER, in chronology, the tenth 

 month of the Julian year, consisting of 

 thirty-one days : it obtained the name of 

 October from its being the eighth month 

 in the calendar of Romulus. See the 

 articles MONTH and YEAR. 



ODE, in poetry, a song, or a composi- 

 tion proper to be sung. Among the an- 

 cients odes signified no more than songs ; 

 but with us they are very different things. 

 The ancient odes were generally compos- 

 ed in honour of their gods, as many pf 

 those of Pindar and Horace. These had 

 originally but one stanza, or strophe, but 

 afterwards they were divided into three 

 parts, the strophe, the antistrophe, and the 

 epode. The priests going round the al- 

 tar singing the praises of the gods, called 

 the first entrance, when they turned 

 to the left, the strophe ; the second, turn- 

 ing to the right, they called antistrophe, 

 or returning ; and, lastly, standing before 



the altar, they sung the remainder, which 

 they called the epode. 



OECUMENICAL, signifies the same 

 with general, or universal ; as oecumeni- 

 cal council, bishop, &c. 



OEDERA, in botany, a genus of the 

 Syngenesia Polygamia Segregata class 

 and order. Natural order of Composite 

 Oppositifolise. Corymbiferix, Jussieu. Es- 

 sential character : calyxes many-flower- 

 ed; corrollets tubular, hermaphrodite 

 with one or two female ligulate florets ; 

 receptacle chaffy ; down of several chaff's. 

 There are two species, viz. O. prolifera, 

 and O. aliena, both natives of the Cape of 

 Good Hope. 



OENANTHE, in botany, dropwort, a 

 genus of the Pentandria Digynia class 

 and order. Natural order of Umbellate, 

 or Umbelliferae. Essential character ; 

 florets diffbrm ; in the disk sessile, bar- 

 ren ; fruit crowned with the calyx and 

 pistil. There are eleven species ; of 

 which O. cjjocata, hemlock water drop- 

 wort, commonly grows four or five feet 

 high, with strong jointed stalks, which 

 being broken emit a yellowish fetid juice ; 

 the leaves are similar to those of hemlock, 

 but of a lighter green colour ; the roots 

 divide into four or five larger taper ones, 

 having some resemblance to parsneps, 

 for which they have been taken. It 

 grows naturally in several parts of Eu- 

 rope, on the banks of ditches, rivers, and 

 lakes. 



OENOTHERA, in botany, treepnmrose t 

 a genus of the Octandria Monogynia class 

 and order. Natural order of Calycanthe- 

 mse. Onagrze, Jussieu. Essential cha- 

 racter : calyx four-cleft ; petals four ; cap- 

 sule cylindrical, inferior; seeds naked. 

 There are eleven species ; of which O. 

 biennis, broad-leaved tree primrose, has a 

 fusiform, fibrous root ; from this, the first 

 year, arise many obtuse leaves, spreading 

 flat upon the ground; from among these, 

 the second year, come out the stems, 

 three or four feet in height, upright, of a 

 pale green colour ; flowers solitary, each 

 being separated by a leaflet, or bracte ; 

 they usually open "between six and seven 

 o'clock in the evening ; for this reason 

 the plant is called evening, or night prim- 

 rose ; the mode of their expanding is cu- 

 rious ; the petals are held together at the 

 top by the hooks at the end of the calyx ; 

 the segments of which first separate at 

 bottom, discovering the corolla, a long 

 time before it acquires sufficient expan- 

 sive force to unhook the calyx at top : 

 when it has accomplished this, it expands 

 almost instantaneously to a certain point ; 



