RA1 



RAI 



Baltic, are attached together in this man- 

 ner, in order to float them off to the ship- 

 ping. The same mode is adopted on the 

 Thames in this country, on the Rhine, 

 and on many of the large lakes and rivers 

 in North America. 



RAGG, rowfez/, in mineralogy, a class of 

 silicious stones, of a dark grey colour, 

 with many shining crystals, having a gra- 

 nu^ar texture, and acquiring an ochry 

 crust, by exposure to the air. The speci- 

 fic gravity is about 2.8. It becomes some- 

 what magnetic by being heated in an 

 open fire. In a strong fire it melts with- 

 out addition, but with more difficulty than 

 bnsaltes. It consists of 



Silica 47.5 



Alumina 32.5 



Iron 20 



100.0 



RAGG stone, in some respects similar 

 to the rowley-ragg. The texture is ob- 

 scurely laminar, or rather fibrous, but the 

 laminse or fibres consist of a congeries of 

 grains of a quartzy appearance, coarse 

 and rough : it effervesces with acids, and 

 strikes fire with the steel : it contains a 

 portion of mild calcareous earth, and a 

 small portion of iron. It is used as a 

 whetstone for coarse cutting tools. It is 

 found about Newcastle, and in several 

 other parts of England, where there are 

 large rocks of it in the hills. 



RAIA, the ray, in natural history, a ge- 

 nus of fishes of the order Cartilaginei. 

 Generic character : five spiracles on each 

 side, placed beneath, near the neck ; 

 mouth beneath the head, transverse, be- 

 set with teeth ; head small, pointed, and 

 not distinct from the body ; :.bocly some- 

 what rhomb oidal. These fishes are found 

 only in the saltwater, where they feed 

 on whatever animal substances they meet 

 with. They are sometimes of the weight 

 of two hundred pounds. They conceal 

 themselves for the greater part of the 

 winter in the mud or sand of the bottoms, 

 and. in consequence of being unprovided 

 with an air bladder, they are seldom seen 

 near the surface of the water. The female 

 is larger than the male, and produces her 

 offspring living, and only one at a time ; 

 the young extricating itself gradually 

 from its confinement, and remaining 

 some time attached by the umbilical ves- 

 sels, after its complete appearance. 

 There are nineteen species. 



R. batis, or the skate, is one of the 



largest of the genus, weighing sometimes 

 two hundred pounds, and one of this size 

 is reported to have been served up at St. 

 John's College, Cambridge, England. It 

 is the most esteemed species of the ge- 

 nus. 



R. clavata, or the thorn-back, is much 

 inferior to the skate in size and goodness. 

 It inhabits the Mediterranean and other 

 seas, and is distinguished by its long and 

 curved spines, on its upper surface. The 

 above are rhomboidal. 



R. pastinaca, or the sting ray, inhabits 

 the Indian and Mediterranean seas, and 

 its tail is armed with a very long serrated 

 spine, with which it can inflict very for- 

 midable wounds, and which it casts off 

 every year. This was formerly supposed 

 to contain the most subtle poison, and an- 

 cient naturalists have been extremely 

 elegant and glowing in their descriptions 

 on this subject. It injures, however, on- 

 ly by piercing and laceration, and, to pre- 

 vent this, the tail is almost always cut oft' 

 as soon as the fish is caught. These fish- 

 es often lie in ambuscade, and seize their 

 prey by surprise, and frequently take it 

 by active and persevering pursuit. 



R. torpedo, the torpedo, inhabits the 

 Mediterranean and the North Seas, and 

 grows to the weight of twenty pounds. 

 This fish possesses a strong electrical pow- 

 er, and is capable of giving a very consi- 

 derable shock through a number of per- 

 sons forming a communication with it. 

 This power was known to the ancients, 

 but exaggerated by them with all the fa- 

 bles natural to ignorance, and it is onlr 

 recently that the power has been ascer- 

 tained to be truly electric. It is conduct- 

 ed by the same substances as electricity, 

 and intercepted by the same. In a mi- 

 nute and a half no fewer than fifty shocks 

 have been received from this animal, 

 when insulated. The shocks delivered 

 by it in air, are nearly four times as strong 

 as those received from it in water. This 

 power appears to be always voluntarily 

 exercised by the torpedo, which occa- 

 sionally may be touched and handled 

 without its causing the slightest agitation. 

 When the fish is irritated, however, this 

 quality is exercised with proportional ef- 

 fect to the degree of irritation, and its 

 exercise is stated, in every instance, to 

 be accompanied by a depression of the 

 eyes. When the animal exerts that be- 

 numbing power from which it derives its 

 name, and when it operates by separate 

 and repeated efforts, this is always the 

 case, both in the continued, and in the 

 instantaneous 4 process, the eyes, which 



