osc 



two-valved, one-flowered ; corolla two- 

 valved, almost equal, growing to the seed. 

 There is but one species, with many va- 

 rieties. Rice has tiie culm from one to 

 six feet in length, annual, erect, simple, 

 round, jointed ; leaves subulate, linear, 

 reflex, embracing, not fleshy ; flowers iu 

 a terminating panicle ; calycine leaflets, 

 lanceolate; valves of the corolla equal in 

 length ; the inner valve even, awnless ; 

 the outer twice as wide, four-grooved, 

 hispid, awned; style single, two-parted. 

 Rice is cultivated in great abundance all 

 over India, where the country will admit 

 of being flooded, and in the southern 

 provinces of China, Cochinchina, Cambo- 

 dia, Siam, and Japan ; in the latter place 

 it is particularly white, and of the best 

 quality. 



OSBECKIA, in botany, so named in 

 honour of Peter Osbeck, a genus of the 

 Octandria Monogynia class and order. 

 Natural order of Calycanthemx. Mclas- 

 tomse, Jussieu. Essential character : ca- 

 lyx four-cleft, with the lobes separated 

 by a ciliary scale ; corolla four-petalled ; 

 anthers beaked ; capsule inferior, four- 

 celled, surrounded by the truncated tube 

 of the calyx. There are two species, 

 viz. O. Chinensis, and O. Zeylanica. 



OSCILLATION, in mechanics, the vi- 

 bration, or reciprocal ascent and descent 

 of a pendulum. See PExnutrM. It is 

 .demonstrated, that the time of a complete 

 oscillation in a cycloid, is to the time in 

 which a body would fall through the axis 

 of that cycloid, as the circumference of a 

 circle to its diameter ; whence it follows : 

 1. That the oscillations in the cycloid are 

 all performed in equal times, as being all 

 in the same ratio to the time in which a 

 body falls through the diameter of the 

 generating circle. 2. As the middle part 

 of the cycloid may be conceived to co- 

 incide with the generating circle, the 

 time in a small arch of that circle will be 

 nearly equal to the time in the cycloid : 

 and hence the reason is evident, why the 

 times in very little arches are equal. 

 3. The time of a complete oscillation in 

 any little arch of a circle, is to the time in 

 Which a body would fall through half the 

 radius, as the circumference of a circle 

 to its diameter: that is, as 3.1416 to 1. 

 If I denote the length of a pendulum,^ = 

 16.J. 1 - = 193 inches, the space a heavy 

 body fails through in the first second of 

 time, and /> = 3. 1416= periphery of a 

 circle whose diameter is 1, then, by the 

 laws of falling bodies, it will 



OSM 



yT , /T 4 is 



T' : V ~ g = 2W/=*nn> 



^/fnearly the time ot falling through \l 



therefore 1 .-/>:: / = : p I > 

 V 2 g * V 2g 



which is the time of one vibration in 

 any arch of the cycloid which has the 

 diameter of its generating circle equal to 



^-/ being the length of the pendulum in 



inches ; and since the latter time is half 

 the time in which a body would fall 

 through the whole diameter, or any 

 chord, it follows, that the time of an os- 

 cillation in any little arch, is to the time 

 in which a body would fall through its 

 chord, as the semicircle to the diameter. 

 4. The times of the oscillations in cycloids, 

 or in small arches of circles, are in a sub- 

 duplicate ratio of the lengths of the pendu- 

 lums. 5. But if the bodies that oscillate 

 be acted on by unequal accelerating 

 forces, then the oscillation will be per- 

 formed in times that are to one another 

 in the ratio compounded of the direct 

 sub-duplicate ratio of the lengths of the 

 pendulums, and inverse sub-duplicate ra- 

 tio of the accelerating forces. Hence it 

 appears, that if oscillations of unequal 

 pendulums are performed in the same 

 time, the accelerating gravities of these 

 pendulums must be as their lengths; 

 and thus we conclude, that the force of 

 gravity decreases as you go towards the 

 equator, since we find, that the lengths of 

 pendulums that vibrate seconds, are al- 

 ways less at a less distance from the equa- 

 tor. 6. The space described by a falling 

 body in any given time, may be exactly 

 known : for, finding by experiments what 

 pendulum oscillates in that time, the half 

 of the pendulum will be to the space re- 

 quired, in the duplicate ratio of the dia- 

 meter of a circle to the circumference. 



OSIER, a very valuable shrub, of the 

 Salix viminales, used principally in bas- 

 ket making. 



OS MITES, in botany, a genus of the 

 Syngenesia Polygamia Frustranea class 

 and order. Natural order of Composite 

 Discoideae. Corymbiferse, Jussieu. Es- 

 sential character : calyx imbricate, scari- 

 ose ; corolla of the ray ligulate ; down 

 obsolete ; receptacle chaffy. There are 

 four species, all shrubs, and natives of 

 the Cape of Good Hope. 



OSMIUM, one of the metals discover- 

 ed by Mr. Tennant, in the black powder 

 which remained after dissolving platina ; 



