

PTO 



parted bristles ; down subplumose ; ca- 

 lyx imbricate. There are eighteen spe- 

 cies, all found at the Cape of Good 

 Hope. 



PTEROSPERMUM, in botany, a ge- 

 nus of the Monadelphia Dodecandria class 

 and order. Essential character: calyx 

 single, five-parted ; corolla five-petalled ; 

 filaments 'fifteen, with five ligules, one 

 between every three filaments ; caosule 

 five-celled, with the cells two-valved ; 

 seeds many, winged. There are two 

 species, viz. P. suberifolium and P. aceri- 

 folium, both natives of the East Indies. 



PTEROTRACHEA, in natural history, 

 a genus of the Vermes Mollusca class and 

 order. Generic character : body detach- 

 ed, gelatinous, with amoveable fin at the 

 abdomen or tail ; two eyes placed within 

 the head. There are four species. 



PTINUS, in natural history, a genus of 

 insects of the order Coleoptera. Generic 

 character: antennse filiform, the last joints 

 larger ; thorax nearly round, not margin- 

 ed, receiving the head. There are about 

 forty species, divided into sections : A. 

 feelers clavate, lip entire. B. feelers fili- 

 form, lip bifid. Of the former section is 

 P. pulsator, or death watch, which is of a 

 dusky colour, with irregular grey brown 

 spots. This insect is found in various 

 parts of Europe in old wooden furniture, 

 makes a peculiar ticking with the fore 

 part of its head, resembling the beating 

 with the nail upon a table ; this is done 

 in several distinct strokes in the night 

 time, and has been considered by the 

 common people as prophetic of some fa- 

 tal occurrence in the family, but is no- 

 thing more than the call of one sex to the 

 other. This must not be confounded 

 with a much smaller insect of a very dif- 

 ferent genus, which makes a sound like 

 the ticking of a watch, and continues for 

 a long time without intermission. This 

 belongs to a different order, and is the 

 Termes pulsatorium of Linnxus. But the 

 real death-watch of vulgar superstition is 

 the ptinus. P. pertinax is brown, imma- 

 culate ; thorax compressed. It inhabits 

 Europe, and is very destructive to wood- 

 en furniture and books. When touched, 

 it draws in its head and legs, and becomes 

 immoveable. An insect strongly allied 

 to this species inhabits the United States, 

 and has generally been considered as the 

 same, but from some of its characters we 

 should suppose it to be specifically dis- 

 tinct. 



PTOLEMAIC, or PTOLEMJEAN system 

 of astronomy, is that invented by Claudius 

 Ptolemy. This hypothesis supposes the 



PTO 



earth immoveably fixed in the Centre, not 

 of the world only, but also of the uni- 

 verse : and that the sun, the moon, the 

 planets, and stars all move about it from 

 east to west, once in twenty-four hours, 

 in the order following, viz. the Moon 

 next to the Earth, then Mercury, Venus, 

 the Sun, Mars, Jupiter, Saturn, the fixed 

 stars, the first and second crystalline hea- 

 vens, and above all th e fiction of their pri- 

 mum mobile. This system, or hypothesis, 

 was first invented and adhered to, chiefly 

 because it seemed to correspond with the 

 sensible appearances of the celestial mo- 

 tions. 



PTOLEMY (CLAUDIUS), in biography, 

 a very celebrated geographer, astrono- 

 mer, and mathematician, among the an- 

 cients, was born at Pelusium, in Egypt, a- 

 bout the seventeenth year of the Christian 

 era, and died, it has been said, in the se- 

 venty-eighth year of his age, and in the 

 year of Christ 147. He taught astrono- 

 my at Alexandria, in Egypt, where he 

 made many astronomical observations, 

 and composed his other works. It is cer- 

 tain that he flourished in the reigns of 

 Marcus Antoninus and Adrian ; for it is 

 noted in his Canon, that Antoninus Pius 

 reigned twenty-three years, which shows 

 that he himself survived him : he also 

 tells us in one place, that he made a great 

 many observations upon the fixed stars at 

 Alexandria, in the second year of Antoni- 

 nus Pius ; and in another, that he observ- 

 ed an eclipse of the moon in the ninth 

 year of Adrian ; from which it is reason- 

 able to conclude, that this astronomer's 

 observations upon the heavens were ma- 

 ny of them made between the year 125 

 and 140. 



Ptolemy has always been reckoned the 

 prince of astronomers among the an- 

 cients, and in his works has left us an en- 

 tire body of that science. He has pre- 

 served and transmitted to us the obser- 

 vations and principal discoveries of the 

 ancients, and at the same time augment- 

 ed and enriched them with his own. He 

 corrected Hipparchus's catalogue of the 

 fixed stars ; and formed tables, by which 

 the motions of the sun, moon, and planets 

 might be calculated and regulated. He 

 was, indeed, the first who collected the 

 scattered and detached observations of 

 the ancients, and digested them into a 

 system, which he set forth in his "Ms yet)w 

 2,vvTet%ix, sive Magna Constructio," di- 

 vided into thirteen books. He adopts 

 and exhibits here the ancient system of 

 the world, which placed the earth in the 

 centre of the universe ; and this has been 



