RH A 



RK 



RETINA'PHTHA. A compound of 

 carbon and hydrogen, formed by dropping 

 resin into a red-hot cylinder. 



RE'TINITE. Retinasphalt. A sub- 

 stance consisting of resin, asphalt, and 

 earth, found at Bovey Tracey adhering to 

 brown coal. 



RETITE'L^ [rete, a net, tela, a web). 

 A family of Spiders, which spin webs of 

 an open mesh-work and of an irregular 

 form, and remain in the middle or on 

 one side, in order to seize their prey. 



RETORT. A globular vessel of glass, 

 or porcelain, with a long neck bended 

 on one side, used for distillation, or de- 

 composition by the application of heat. 



RE'TROGRADE {relro, backward, 

 gradior, to go). A term used in Astro- 

 nomy, in opposition to direct. Thus, all 

 motion from east to west, as the apparent 

 motion of the heavens, is retrograde; 

 while the earth's diurnal motion, which 

 causes it, is direct. 



REU'SSITE. A substance consisting 

 of several sulphates, and occurring in 

 the form of a mealy efflorescence on the 

 surface of the earth about Seidlitz and 

 Seidschutz. 



REVERBERATORY FURNACE 

 That kind of furnace, in which the flame 

 is driven back, or prevented from 

 rising. 



REVERSE SHELLS. Shells which 

 have the aperture opening on the left 

 side when placed in front of the spec- 

 tator. 



REVERSION OF SERIES. A term 

 sometimes confounded, in Mathematics, 

 with inversion. Tims, the connexion 

 of the square root with the square is 

 described as inverse ; but if y be a given 

 series of powers of x, the determination 

 of ar in a series of functions of y is not 

 called inversion, but reversion. 



REVIVIFICATION (revivisco, to be- 

 gin to live again). In Chemistry, this 

 term has been applied to the reduction of 

 metals. In natural history, it denotes a 

 phenomenon which occurs in some ani- 

 malcules, as the rotifer redivivus, which 

 lives in water, but, after remaining for 

 years in a dry state, with all its functions 

 suspended, revives in a few minutes on 

 being placed in water. 



REVOLUTION. In pure mathema- 

 tics, this term denotes an angle moved 

 over by a line which revolves round a 

 point from any one position to that posi- 

 tion again. It is, therefore, a synonj-m 

 for four right angles. 



RHAMNACEiE. The Buckthorn tribe 

 288 



of Dicotyledonous plants. Trees or 

 shrubs with leaves alternate ; flowers ax- 

 illary or terminal, polypetalous ; petals 

 cucullate ; stamens perigynous ; ovarium 

 superior ; seeds albuminous. 



RHINOLOPHI'N^ {plv, the nose, 

 \60of, a crest). A family of the insec- 

 tivorous Cheiroptera, named from the 

 peculiar form of the anterior nasal ap- 

 pendage, and including the greater and 

 lesser horse-shoe bats of our own coun- 

 try. 



RHIPI'PTERA (p/TTk, a fan, Trrepiv, 

 a wing). Fan-winged insects ; an order 

 of insects, which have only one pair of 

 wings fully developed, and these are on 

 the metathorax ; the other pair are rudi- 

 mentary. See Diptera. 



RHI'ZANTHS {pi^a, a root, fiv^op, a 

 flower). A class of parasitical leafless 

 plants, which, with many of the pecu- 

 liarities of Endogens, seem to constitute 

 an intermediate form of organization 

 between them and the loiver Acrogens. 

 They are all of a fungus-like consistence, 

 with few traces of a vascular system ; the 

 flowers are propagated by the agency of 

 sexes ; the seeds have no embryo, but 

 consist of a homogeneous sporuliferous 

 mass. 



RHIZOCA'RPOUS {pi^a, a root, Kag- 

 TTor, fruit). A botanical term applied to 

 those polycarpous fruits, whose root en- 

 dures many years, but whose stems 

 perish annually, as herbaceous plants. 



RHIZOME {piCoona, that which has 

 taken root). A root-stock, or root-like 

 stem, which lies prostrate on the ground, 

 and emits roots from its under side, as 

 in iris. 



RHODIUM {podov, a rose). A new 

 metal discovered in the ore of platinum, 

 and named from the red colour of one of 

 its solutions. 



RHODIZONIC ACID (podov, a rose). 

 An acid derived from carbonic oxide, and 

 named from the red colour of its 

 salts. 



RHO'DONITE. A fibrous ore of man- 

 ganese, consisting of silica and the prot- 

 oxide of manganese. 



RHOMB-SPAR. A variety of man- 

 ganesian limestone, composed of the car- 

 bonates of lime and of magnesia, and 

 occurring imbedded in chlorite slate, 

 limestone, &c. It has been called bitter 

 spar and muricalcite. 



RHOMBOID (po/i/3o9, a rhombus, 

 elao?, likeness). A four-sided figure, 

 which has its opposite sides equal to one 

 another, but all its sides are not equal, 



