P Y R 



282 



P Y T 



Pythago- 

 ras. 



Pyroxene PYROXENE, or AUGITE, the name of a mineral 

 which has already been described under MINERALOGY, 

 Vol. XIV. p. 537. 



Since that article was written, a very complete ana- 

 lysis of the Pyroxenes has been made by M. Henry 

 Rose. From this analysis, it follows that the mineral 

 called Pyroxene, when it is uncoloured, is a double 

 bisilicate of lime and magnesia, containing an atom of 

 each; but that when it is coloured, it consists of a 

 mixture of bisilicate of lime, of bisilicate of magnesia, 

 of bisilicate of the protoxide of iron, and, less frequent- 

 ly, of bisilicate of the protoxide of manganese : without 

 these bases being combined in proportions conformable 

 to the theory of definite proportions. The only thing 

 constant is, that all the bases belong to the same iso- 



morphous * class, and that they are all in the form of Pytfoago- 

 bisilicates. ras. 



One of these pyroxenes, analysed by M. Rose, was ^*'~s^**- / 

 found to be a double bisilicate of lime, and of protoxide 

 of iron, containing an atom of each of these bases. This 

 pyroxene has been called Hedenbergite, and has been 

 considered, after the analysis of M. Hedenberg, as a, 

 bisilicate of the protoxide^of iron. Another has been 

 found to be composed almost entirely of the bisilicate of 

 the protoxide of manganese, with a very little of the 

 bisilicate of lime. 



The following table contains the numerical results 

 of M. Rose's analysis, from which it will be seen, that 

 in every case the silex contains twice as much oxygen 

 as the bases together. 



PYRRHONIANS, or PYRRHONISTS, the name of 

 a sect of ancient philosophers, founded by the Greek 

 philosopher Pyrrho, who died in the ninetieth year of 

 his age, about the year 288 B. C. The principle of the 

 Pyrrhonists was to doubt of every thing ; and they 

 maintained, that we judge of what is true or false only 

 from appearances, which deceive us. See Brucker's 

 History of Philosophy, vol. i. 



PYRRHUS. See EPIRUS, Vol. IX. p. 187, 188. 



PYRUS. See BOTANY and HORTICULTURE, Vol. 

 IX. p. 208, 211. 



PYTHAGORAS, a celebrated ancient philosopher, 

 and founder of the Pythagorean school, was born at 

 Samos, in the fifth or sixth century before Christ. He 

 was the son of a lapidary, and received the first ele- 

 ments of education from Cresphilus. He afterwards 

 went to the island of Scyrus to study under Pherecy- 

 des, and he is said to have returned to Samos to resume 

 his education under his first master. 



Although the early history of Pythagoras is involved 

 in fable, yet it is certain that he travelled into Egypt 

 to study the arts and sciences of that enlightened coun- 



try. Having been introduced to Amasis, king or. 

 Egypt, by Polycrates, tyrant of Samos, he was admit- 

 ted to the colleges of the Egyptian priests, having pre- 

 viously performed several troublesome ceremonies, a- 

 mong which was that of circumcision. In these sanc- 

 tuaries of knowledge he studied, for twenty-two years, 

 the astronomy and geometry of the Egyptians, and 

 made himself master of all the opinions and facts which 

 were involved in the mysteries of that singular people. 

 Pythagoras is said to have travelled to Chaldea, and 

 to different parts of the east ; but there does not seem 

 to be any good evidence for this opinion, and we are 

 disposed to agree with Brucker in thinking that he re- 

 turned directly to Samos, loaded with the intellectual 

 treasures which he had amassed, and eager to share 

 them with his own countrymen. The Samians, how- 

 ever, were not disposed to appreciate the gift which 

 was thus nobly offered to them. Pythagoras abandon- 

 ed his attempt to institute a school for their instruc- 

 tion ; and repairing to Delos, where he presented an of- 

 fering to Apollo, he pretended to have received from 

 the priestess certain moral precepts, which, with this 



The very interesting discovery of isomorphous bodies we owe to that eminent chemist, Professor Mitscherlich of Berlin. He found that 

 several substances, simple as well as compound, may replace one another in compound bodies, without any change of form taking place in 

 the latter, provided that the other constituent principles remain the same, and in the same proportions. Phosphorus and arsenic, for exam- 

 ple, replace one another, so that the phosphates crystallize in exactly the same manner as the arseniates of the same bases, when they are at 

 the same poi'nt of saturation, and contain the same number of atoms of water of crystallization, which is generally the case. Arsenic and 

 phosphorus are therefore called isomorphous bodies. See Kongl Velenslcaps Academicns Handlingar, for ar. 1821, p. 4. 



