EPICYCLE EPIDOTE. 



67 



is left of his numerous writings. Some fragments 

 of a Treatise on Nature have been found at Hercu- 

 laneum, and published by Orelli (Leipsic, 1818.) 

 The other accounts of his philosophy are only the 

 poem of Lucretius, and the notices of it in Cicero, 

 Pliny the elder, &c., and two letters, (published by 

 Schneider, Leipsic, 1813, in a revised and improved 

 edition). An epicurean, according to the perverted 

 meaning of the epicurean doctrine, is one who is 

 devoted to sensual enjoyments, particularly those of 

 the table. 



EPICY'CLE, hi the ancient astronomy, was a sub- 

 ordinate orbit or circle, which was supposed to move 

 on the circumference of a larger one, called the dif- 

 ferent ; by means of which one motion, apparently 

 irregular, was resolved into two that were circular 

 and uniform. And when the observed motion was 

 so irregular and complicated as not to be resolved 

 with one epicycle, others were added, till a nearer 

 approximation was obtained. This system owed its 

 origin to a prejudice that seems to have been ex- 

 tremely ancient, in favour of circular motion ; and 

 the problem that principally engaged the attention 

 of astronomers in those times, was to assign the pro- 

 per proportion of the different and epicycle which 

 should approximate nearest to absolute observation. 

 See Astronomy, History of. 



EPICYCLOID, in geometry, is a curve generated 

 by a point in one circle, which revolves about 

 another circle, either on the concavity or convexity of 

 its circumference, and thus differs from the common 

 cycloid, which is generated by the revolution of a 

 circle along a right line ; though the latter has some- 

 times been assimilated with the former, by consider- 

 ing the right line as the circumference of a circle 

 whose diameter is infinite. The invention of epicy- 

 cloids is ascribed to M. Roemer, the celebrated 

 Danish astronomer. 



EPIDAURUS ; one of the most considerable 

 towns and commercial seaports of ancient Greece ; 

 situated in Argolis, in the Peloponnesus ; particularly 

 celebrated for its magnificent temple of .^Esculaphis, 

 which stood on an eminence not far from the town. 

 An inscription over the entrance declared it to be 

 open only to pure souls. Crowds of invalids resorted 

 to the place, hi hopes of obtaining a cure from the 

 beneficent divinity, in whose honour festivals were 

 celebrated yearly. 



EPIDEMIC, or EPIDEMIC DISEASE (from 

 liri and lfi>s, among the people), signifies a state of 

 sickness which prevails in a place or tract of country 

 only for a temporary period. An epidemic always 

 originates in transient external influences, which gra- 

 dually produce such clianges in the bodily system, as 

 finally bring on the sickness. Thus many diseases 

 appear to arise from some peculiar morbid-matter in 

 the atmosphere, brought by particular winds; e. g., 

 the influenza, and other diseases : also, poor or scanty 

 food, unwholesome mixtures, &c., may occasion 

 epidemics. Seasons of scarcity, which compel men to 

 have recourse to unusual means of subsistence, (as, 

 for example, in Norway and Sweden, to the bark of 

 trees instead of corn), often occasion epidemics. 

 The ergot in rye is supposed to be the cause of ra- 

 pkania. Bad barley, or much mixture of bearded 

 darnal (lolium temulentum) , makes the beer which 

 is prepared from it unwholesome, and produces sick- 

 ness in those who partake of it. Causes producing 

 a disturbed state of mind, such as war, sieges, earth- 

 quakes, &c., by their effects on the nervous system, 

 may very much favour the production of epidemic 

 diseases, or at least render them more malignant. 

 Epidemics sometimes begin with a few, sometimes 

 attack great numbers at once, as commonly happens 

 in a great and sudden change of wind or weather. 



If, for instance, after a long continuance of a west 

 or south-west wind, with warm weather, it suddenly 

 changes to an east or north-east wind, we hear peo- 

 ple complaining directly of coughs, colds, rheuma- 

 tisms, &c. An epidemic, at its commencement, is 

 usually mild, and becomes more dangerous as it 

 spreads ; as it goes off, it, for the most part, assumes 

 a mild character again. It frequently terminates as 

 gradually as it began, but sometimes suddenly. 

 Many persons are not at all affected by the prevailing' 

 epidemic. The cause probably lies in their bodily 

 habit, which is opposed to the prevailing influences, 

 and makes them capable of resisting them longer 

 than other persons. Thus it often happens that men 

 with chronic complaints, hypochondriacs, &c., remain 

 free from epidemic disorders. Epidemics are often con- 

 founded with contagious disorders. The first originally 

 are not contagious; their origin and propagation 

 depend on general influences, and they commonly 

 generate no contagious matter, producing the same 

 disease in another body by contact with it. It is 

 only in particular circumstances, especially if the 

 disorder is a violent one, and many patients are 

 crowded into a narrow room, that a contagious mat- 

 ter can lie generated, forming a corrupt atmosphere 

 about the sick, and capable of exciting the disease in 

 persons who come near it. Even under these cir- 

 cumstances, contagion does not necessarily take 

 place, and the ignorant generally conceive a hasty 

 and groundless fear of contagion. Thus, for in- 

 stance, that is frequently ascribed to contagion, which 

 is only the consequence of a violent shock of the 

 nervous system at the sight of a sick person, perhaps 

 in a loathsome state, whereby the disease, to which 

 the body was already disposed, is more quickly de- 

 veloped. 



EPIDERMIS (from \v">, upon, and ligpx, the true 

 skin); the scarf-skin. See Cuticle, and Skin. 



EPIDOTE. This mineral is found crystalized in 

 rhombic prisms variously modified, both laterally and 

 at its extremities. It cleaves parallel to the sides of 

 a right-oblique-angled prism of 1 15 36', and 64 

 24', which is therefore its primary crystal. Some of 

 its more interesting secondary or actually occurring 

 forms are the following, viz. : 1. the primary crystal, 

 altered by the truncation of its acute lateral edges, 

 and terminated at both extremities by dihedral sum- 

 mits ; 2. the same, but terminated by four-sided 

 pyramids, whose apices are truncated; 3. the pri- 

 mary crystal, with all its lateral edges truncated and 

 terminated as in the last instance. The prisms are 

 generally streaked longitudinally ; lustre, vitreous ; 

 colour, green and gray prevalent. Among the 

 most common shades of the first is pistachio-green ; 

 the gray colours pass into white ; translucent on the 

 edges, and sometimes transparent ; brittle ; hard- 

 ness above that of feldspar, and little inferior to 

 quartz ; specific gravity, 3.26 to 3.42. Some of the 

 larger crystals from Norway consist of concentric 

 coats, the outer ones of which, being peeled off, 

 leave a crystal with smooth faces. Thin crystals 

 are often observable. When massive, the individu- 

 als are columnar, straight, and either parallel or di- 

 vergent ; they are sometimes granular, and even 

 become, occasionally, impalpable, when they are 

 strongly connected. The deep green varieties are 

 called, in common language, epidote, while the gray 

 are denominated zoitite ; no distinction exists be- 

 tween the two, except what arises out of colour. 

 The granular variety has also been distinguished by 

 the separate appel'ation of scorza ; and a light reddish- 

 black variety from Piedmont, which is highly charged 

 with oxide of manganese, has been called the man 

 ganesian epidote. The chemical composition of epi- 

 dote is as follows, the specimen analyzed consisting of 



a 



