PCS 



POT 



the close of the last century, when, in 

 order to meet the increased expences of 

 every portion of the undertaking, it was 

 determined to double the charge, and 

 from that period it received the denomi- 

 nation of the two-penny post. In order 

 to facilitate the conveyance of letters and 

 packets, boys are employed, who ride 

 small swift horses to and from the prin- 

 cipal office, situated in Gerard-street, 

 Soho, where may be seen a miniature 

 copy of the proceedings at the general 

 post-office, already described. 



POST-q^?ce, a general post office was 

 erected 12 Charles II. c. 35. It was 

 made perpetual, and part of the general 

 fund, 3 George I. c. 7. The postmaster 

 is not like a common carrier, and is not 

 answerable for the loss of any money by 

 post, nor can the country postmaster add 

 any charge to the postage for carrying the 

 letters out to the inhabitants of the town. 

 The case has been several times tried and 

 decided. A principal object in the erec- 

 tion of the post-office, was in order to 

 have the means of inspecting letters of 

 individuals, and discovering attempts 

 against the Government, (see the Ordi- 

 nance 1657); and now letters may be 

 opened by an order from a Secretary of 

 State. For this, and other purposes, 

 there are several penalties levied upon 

 persons carrying or sending letters by 

 private conveyance. Letters coming by 

 private ships from abroad, and even let- 

 ters belonging to the owners, must also 

 pass through the post office. 



POST, in the military art, is any place 

 or spot of ground, fortified or not, where 

 a body of men may make a stand and for- 

 tify themselves, or remain in a condition 

 to fight an enemy. Hence it is said, that 

 the post was relieved, the post was taken 

 sword in hand, &c. 



POST, advanced, is a spot of ground 

 seized by a party to secure the army, and 

 cover the posts that are behind. 



POSTERN in fortification, is a small gate 

 generally made in the angle of the flank 

 of a bastion, or in that of the curtin, or 

 near the orillon, descending into the 

 ditch ; by which the garrison may march 

 in and out unperceived by the enemy, 

 either to relieve the works, or to make 

 private sallies, &c. 



POST1L, a name anciently given to a 

 note in the margin of the bible, and after- 

 wards to one in any other book posterior 

 to the text. 



POSTING, among merchants, the put- 

 ing an account forward from one book to 



another, particularly from the journal or 

 waste-book to the ledger. 



POSTULATE, in mathematics, &c. is 

 described to be such an easy and self-evi- 

 dent supposition, as needs no explication 

 or illustration to render it intelligible ; as, 

 that a right line may be drawn from one 

 point to another. That a circle may be 

 described on any centre given, of any 

 magnitude, &c. ; however, authors are 

 not well agreed as to the signification of 

 the term postulatum ; some make the dif- 

 ference between axioms and postulata to 

 be the same as that between theorems 

 and problems ; axioms, according to those 

 authors, being truths that require no de- 

 monstration. But others will have it, that 

 axioms are primitive and common to all 

 things, partaking of the nature of quanti- 

 ty, and which therefore may become the 

 objects of mathematical science ; such as 

 number, time, extension, weight, motion, 

 &c. and that postulata relate particularly 

 to magnitude, strictly so called, as to 

 things having local extension, such as 

 Hues, surfaces, and solids ; so that in this 

 sense of the word postulatum, Euclid, be- 

 sides axioms, or those principles which 

 are common to all kinds of quantities, has 

 assumed certain postulata to be granted 

 him peculiar to extensive magnitude. 

 Hence several of the principles assumed 

 in his Elements, and ranked among the 

 axioms by the moderns, are by Proclus 

 ranked among the postulata, which has 

 induced Dr. Wallis to judge, that the last 

 of the two senses given to the term pos- 

 tulatum is most agreeable to the meaning 

 of the ancient geometers. 



POSTURE, in painting and sculpture, 

 the situation of a figure with regard to the 

 eye, and of the several principal members 

 thereof with regard to one another, 

 whereby its action is expressed. A con- 

 siderable part of the art of a painter con- 

 sists in adjusting the postures, in giving 

 the most agreeable postures to his figures, 

 in accommodating them to the characters 

 of the respective figures, and the part 

 each has in the action, and in conducting 

 and pursuing them throughout. 



POTAMOGETON, in botany, pond* 

 weed, a genus of the Tetranclria Tetragy- 

 nia class and order. Natural order of In- 

 undatse. Naiades, Jussieu. Essential 

 character: calyx none; petals four; 

 style none ; seeds four. There are four- 

 teen species ; these are perennial, her- 

 baceous plants, inhabitants of the wa- 

 ter. 



POTASH, in chemistry, a substance 



