I'YR 



PYR 



that though they differ in the method of 

 description, that each author has been 

 correct in stating 1 the facts relating to 

 them. Denon concludes his detail \vitli 

 several just and severe observations on 

 the pride of those by whose order they 

 were erected, and the barbarous igno- 

 rance and stupidity which governed those 

 who obeyed its dictates ; and yet, strange 

 as it may appear, it becomes necessary to 

 mention a pyramid erected by the very 

 Frenchmen, who, having 1 visited Egypt, 

 and witnessed the effects of ancient des- 

 potism, perversely imitated the devotion 

 of its inhabitants to a military idol, who 

 has wofully convinced the world how lit- 

 tle that devotion is deserved. 



The pyramid alluded to is situated in 

 Holland, was designed by the chief of the 

 battalion of engineers of the French ar- 

 my there, is 1 10 French feet high, exclu- 

 sive of an obelisk on the summit, which is 

 42 feet more ; aud the sides have four in- 

 scriptions, three adulatory, and the last 

 to the following' purport : " This pyra- 

 mid was raised to the august Emperor of 

 the French, Napoleon the First, by the 

 troops encamped in the plain of Zeyst, 

 being 1 a part of the French and Batavian 

 army, commanded by the Commander in 

 Chief, M armont." As 30,000 men assist- 

 ed in this undertaking, it was completed 

 in 32 days, in the year 12, by their com- 

 putation. 



PYRAMID, in geometry, a solid, stand- 

 ing on a triangular, square, or polygonal 

 basis, and terminating in a point at the 

 top ; or, according to Euclid, it is a solid 

 figure, consisting of several triangles, 

 whose bases are all in the same plane, 

 and have one common vertex. 



Hence the superficies of a given pyra- 

 mid is easily found by measuring these 

 triangles separately ; for their sum added 

 to the area of the base is the surface of 

 the pyramid required. It is no less easy 

 to find the solid content of a given pyra- 

 mid ; for the area of the base being found, 

 let it be multiplied by the third par}; of the 

 height of the pyramid, or the third part 

 of the base by the height, and the pro- 

 duct will give the solid content, as is de- 

 monstrated by Euclid, lib. 12. prop. 7. If 

 the solid content of aifrustrum of a pyramid 

 is required, first let the solid content of 

 the whole pyramid be found ; from which 

 subtract the solid content of the part that 

 is wanting, and the solid content of the 

 frustrum,or broken pyramid, will remain. 

 Every pyramid is equal to one third of its 

 circumscribing prism, or that has the 

 same base and height ; that is, the solid 



content of the prism is equal to one thin! 

 of the prism For supposing the base a 

 square, then does the pyramid consist of 

 an infinite number of such squares, whose 

 sides, or roots, are continually increasing' 

 in arithmetical progression, beginning at 

 the vertex or point, its base being the 

 greatest term, and its perpendicular 

 height the number of all the terms : but 

 the last term multiplied into the number 

 of terms will be triple the sum of all the 

 series, equal the solid content of the py- 

 ramid. 



All pyramids are in a ratio compound- 

 ed of their bases and altitudes ; so that if 

 their bases be equal, they are in propor- 

 tion to their altitudes ; and vice vwsa. 

 Equal pyramids reciprocate their bases 

 and altitudes; that is, the altitude of one 

 is to that of the other, as the base of the 

 one is to that of the other. 



PYRITES. Iron, in combination with 

 sulphur, forms a mineral substance, which 

 has been long kno\vn under the name of 

 Pyrites, and which is very extensively dif- 

 fused. It occurs massive, dissemimued, 

 and frequently crystallized : the forms of 

 its crystals are various, but the most com- 

 mon is the cube regular, or modified by 

 truncation of the angles or edges, or ac- 

 cumination of three planes on the angles: 

 the octaedron, clodecaedron, and icosae- 

 dron, also sometimes occur. 



Its colour is brass-yellow, varying a lit- 

 tle in the shade, and the lustre is always 

 fully metallic : it is opaque. The frac- 

 ture is uneven. It is brittle ; its hardness 

 is such as to strike fire with steel ; its spe- 

 cific gravity is from 4.6 to 4.8. By fric- 

 tion it exhales a sulphurous smell. This 

 odour is strong when it is heated before 

 the blow-pipe ; it gives at the same time 

 a blue flame ; and at length a globule of a 

 brownish colour. It is soluble in nitric 

 acid, with the disengagement of red va- 

 pours. It is not sensibly magnetic. Va- 

 rious analyses of it have been given : ac- 

 cording to those executed by Mr. Hatch- 

 et, it consists of 



Sulphur 52 



Iron 48 



100 



Besides this, which may be named com- 

 mon Pyrites, there are some others which 

 may be regarded as varieties of the spe- 

 cies, and which differ principally in struc- 

 ture, or in the form under which they 

 occur. The striated or radiated pyrites 



