PARABOLOID 



PARADISE-FISH 



747 



From the above property it is easy to prove that 

 PN 2 = 4AS'AN, where N"is the foot of the perpen- 

 dicular from P upon OA. It is obvious that the 

 parabola is not a closed curve. The centre (cor- 

 responding to the centre of the ellipse) is situated 



at infinity. The 

 tangent to the 

 curve at P bisects 

 the angle SPD. 

 Hence a reflecting 

 surface formed by 

 the revolution of 

 PAP' about OA as 

 axis is such that 

 parallel rays falling 

 upon it in the 

 direction of OS are 

 reflected to S. 

 Conversely, rays 

 diverging from S 

 will be reflected 

 parallel to SO. 

 Hence the intensity 

 of the reflected 

 beam of light re- 

 mains constant at 

 all distances from the source, except in so far as it 

 is affected by absorption, and the parabolic is 

 therefore the most perfect form of reflector (see 

 LIGHTHOUSE, REFLECTION ). If the resistance of 

 the air were negligible, the path of a projectile 

 would approximately be a parabola with its axis, 

 or principal diameter, vertical, and its vertex at 

 the highest point of the path. Let PN = y, 

 AN = x, AS = a. The equation of the parabola 

 referred to its vertex as origin is y 1 = tax. All 

 curves the equations of which are of the form 

 y* = />" are classed as parabolas. Thus, the curve 

 represented by the equation y'' = px is called the 

 cubical parabola ; and that one whose equation is 

 y 3 = pi? is called the semi-cubical parabola. 



Paraboloid is a solid figure traced out by a 

 Parabola (q.v.) revolving round its principal axis. 



Paracelsus, a name coined for himself by 

 Theophrastus Bombastus von Hohenheim, was 

 apparently meant to imply that he was greater 

 than Celsus ; there is no good authority for Further 

 adding the names Philippus Aureolus. Paracelsus 

 was the son of Wilhelm Bombast von Hohenheim, 

 a physician at Einsiedeln, in the Swiss canton of 

 Scliwyz, and was born in 1490, 1491, or 1493 

 (it se'ems impossible to decide which). He owed 

 his early education mainly to his father ; went to 

 Basel University at sixteen, but soon left to study 

 alchemy and chemistry with Trithemius, Bishop of 

 Wiirzburg ; and next at the mines in Tyrol belong- 

 ing to the Fugger family learned the physical 

 properties of metals and minerals, and the dis- 

 position of rock strata, and began to realise 

 that the olwervation of nature is of surpassingly 

 greater value to the student than academic pre- 

 lections or the lucubrations of the study. Here 

 and in subsequent wanderings over great part of 

 Europe he amassed a vast store of facts, learned the 

 actual practice of medicine amongst various peoples, 

 but lost all faith in scholastic disquisitions and 

 disputations. He acquired no little fame as a 

 medical practitioner, and on his return to Basel in 

 1526 received the appointment of town physician. 

 He also lectured on medicine at the university, 

 Irat defied academic tradition not merely by lectur- 

 ing in German (not Latin ), but by flouting at Galen 

 and Avicenna bu/ning their books in public, it was 

 affirmed and denying all that was most firmly 

 believed by the faculty. 



Bitterness, backbiting, enmities soon rose and 

 pursued him throughout the rest of his life, 



aggravated and justified in some measure by his 

 own vanity, arrogance, and aggressiveness, as also 

 by his intemperate habits. A dispute with the 

 magistrates in 1528 led to his leaving Basel in 

 haste ; he wandered for more than a dozen years, 

 visiting Colmar, Nuremberg, Zurich, Augsburg, 

 and many other towns, but seldom sojourning 

 more than a few months, and at last settled in 

 1541 under the protection of the archbishop at 

 Salzburg. But he died on the 24th September of 

 the same year murdered by his enemies, said his 

 friends ; in consequence of a drunken debauch, 

 said his enemies. 



He is said to have written some 364 works, of 

 which only some 230 were printed ; and of these 

 the critics only admit from ten (Marx) to twenty- 

 four (Haser) as genuine, the others being by his 

 followers the ' Paracelsists. ' They were mainly 

 written in Swiss-German, the Latin versions being 

 by other hands. About a dozen were translated 

 into English. The earliest printed work was Prac- 

 tica D. Theophrasti Paracelsi (Augsburg, 1529). 

 Collected German editions appeared at Basel in 

 1589-91 (11 vols. 4to) and again in 1603-5 (4 vols. 

 folio; re-issued 1618), Latin editions in 1603-5 

 (11 vols. 4to) and 1658 (Geneva, 3 vols. folio). 



His system was based on a cosmogonic view of 

 the universe, the disturbances in the economy of 

 the human microcosm corresponding to and being 

 determined by the movements of the all-embracing 

 macrocosm. Repudiating the current pseudo- 

 Aristotelianism, Paracelsus turned sympathetically 

 to Neoplatonism and the Cabbala ; but it seems 

 difficult not to admit in him an element of pure 

 charlatanism, as well as of mysticism. Unquestion- 

 ably, however, his method and his influence tended 

 in the direction of the immediate observation of 

 nature, the discarding of antiquated theories, the 

 encouragement of independent research, experi- 

 ment, and innovation. He is not to be blamed 

 for clinging like his age to Alchemy (q.v.); he 

 certainly made some new chemical compounds, and 

 applied chemical knowledge to improve pharmacy 

 and therapeutics, and, in an empirical fashion, to 

 revolutionise hide-bound medical methods. 



See monographs by M. B. Lessing (1839), Marx (1842), 

 Mook ( Wurzburg, 1876) ; the article MEDICINE ; and the 

 History of Medicine by Haser. There is an English Life 

 of Paracelsus by Fr. Hartmann ( 1886 ) ; Browning's 

 famous poem on Paracelsus is well known. 



Parachute (Fr. chide, 'a fall'), a machine 

 for the purpose of retarding the velocity of descent 

 of any body through the air, and employed by 

 aeronauts as a means of descending from Balloons 

 (q.v.). The original type was a gigantic umbrella, 

 strongly made, and having the outer extremities 

 of the rods, on which the canvas is stretched, firmly 

 connected by ropes or stays to the lower part of 

 the handle. It was recommended in 1783 at Lyons 

 by Le Normand as a means of escape from a house 

 on fire, but was first used in connection with 

 ballooning by Blanchard in 1793. In 1887 Baldwin 

 claimed to have descended from a height of one 

 mile by means of a parachute in 3$ minutes. 



Paraclete. See SPIRIT (HOLY), MONTAN- 

 ISM, ABELARD. 



Paradise ( Gr. paradeisos, ' a park,' ' a pleasure- 

 ground ;' originally an oriental, apparently Persian, 

 word ; cf. the Heb. pardes, and modern Persian, 

 Jirdaus), the garden of Eden (q.v.), Heaven (q.v.). 

 See BIRD OF PARADISE for the bird so named. 



Paradise-fish (Macropodus viridi-auratus), a 

 Chinese species of Macropod often kept in aquaria 

 for its beauty of form and colouring. In the male 

 the colours increase in brilliancy at the pairing- 

 season, and he swims around his wished-for mate, 

 fluttering the long, delicate filaments of the ventral 



