193 



P. 



PACKING-PRESS. 



191 



Pis the tenuia or thin letter of the labial series. For the various 

 symbols employed to denote this letter see ALPHABET. 

 This letter is interchangeable with those which belong to the same 

 organ, that is the lips, and with some others. Thus, 



1. P is convertible with a 6. The Latin, like the Welsh, was fond of 

 the thin letters, in consequence of which there are very few words in 

 that language which begin with b, while those commencing with p 

 form a numerous class. It will often be found that the p in Latin 

 words becomes a 4 in the related languages. Thus apicula, the diminu- 

 tive of apit, a bee, is in French abeille ; tepten is in German sieben. 

 The German language often confounds 6 and p, more particularly when 

 the former is final. Perhaps, too, even in Latin, the written 6 was pro- 

 nounced as a p in the prepositions ab, ttih, o/j, which correspond to the 

 Greek airo, UJTO, en. 



2. P with m, somewhat rare. Thus the Greek preposition /itra is 

 in the Jiolic dialect rcSa. Again, the Greek nu\v8Sos is essentially 

 the same word with the Latin plumbut. Allied to this change is the 

 insertion of a p between either m and or m and I, as in the Latin 

 sumpgi, sumptus, for xumsi, xitmtus, and temptare for tentare. 



3. P with v. This change is more particularly to be observed in the 

 derivation of French from Latin. Thus, from capiUus, hair, epitcopug, 

 a bishop, dedpere, deceive, &c., aperire, open, opera, work, lepia, hare, 

 pauper, poor, piper, pepper, Aprilit, April, the French have deduced 

 their cheveu, ectque, tleeeroir, &c., oum'r, (tuvre, Mrre, paurre, poivre, 

 Arril. 



4. P with /. Two or three examples are given under F. To these 

 may be added pro, fur ; pater, father ; piscii, Jinh. ; pauci, few ; Input, 

 wolf. So .the Greek ropipvpa, q>cum\i), *oiyi{, have the aspirate, 

 while the Latin, as usual, prefers the tenuis in purpura, pcenitla, 

 Poenu*. 



5. P with pf. The latter form is often preferred by the German, 

 where our own tongue has the single letter. Thus the English words 

 pound, peach, pepper, pea-cock, penny, ajiple, are written by the Germans 

 pfund. p/irtche, pfeffer, pfau, pfenniy, apfd. 



6. P with e, k, or q. See C. 



7. P with t, as TOJ, in Latin poro. The Greek interrogative words 

 beginning with a T, as rov, wr/, war f pas, &c., are related on the one hand 

 to the Ionic forms KOU, oj, Konpos, and on the other to the demon- 

 stratives that commonly take a T at the beginning. And in fact the 

 latter are often used as relatives. 



8. P with pt. The latter is common in Greek, as in TUTTM, 

 oin-ojuai, 4c., which form their other tenses for the most part without 

 a T. So too at the beginning of words. Thus irroAn and irroAe>os 

 coexist with ToXn and *o\tuot ; and it seems probable that it was an 

 unsuccessful attempt to pronounce the initial pt which led to the 

 formation of the Latin words popttlui, a state, and popular!, to devastate 

 with war. 



9. Pi with ip. This change it will be more convenient to consider 

 under the letter S. 



10. Pi before a vowel with eh. Thus tapiam, in Latin, becomes 

 lac/ie in French. The word roche, too, was probably formed from a 

 barbarous Latin word ru/iiit ; and Rut upturn, in the county of Kent, 

 appears upon this principle to have changed its named to Rich- 

 boruugh. 



PAVE(Pattut), a measure ef the Koman system, being in fact their 

 unit of itinerary measure, to which the millc paitut, or MILE, was 

 referred. Thi' word pattus is connected with the root of patulere, to 

 extend, and Paucton curiously enough derives it a patfii mauibut, from 

 the length between the extended hands, instead of a pastil pedibiu. 

 There is however reason to believe that the mille passus came into use 

 from the practice of measuring distances in new countries from the 

 number of paces marched by the soldiery, of which a rough reckoning 

 was kept, but whether by actually counting the paces, or by the time 

 of marching compared with the previously known number of paces in 

 a given time, ii not known. It is well known that with disciplined 

 soldiers either method would give very good practical results. Vitru- 

 viua describes a machine to be fastened to the wheel of a chariot (an 

 invention revived in our own day), by which its number of revolutions 

 was registered ; but this was probably a late invention. 



The pace was not, as persons in general suppose, the step or the 

 dirtance from heel to heel when the feet are at their utmost ordinary 

 extension ; this, which the French metrologists call pat simple, was the 

 yradut or </rauu. The passus, or pat double of the same writers, was 

 two gradus, or the distance from the point which the heel leaves to 

 that on which it is set down. Assuming the Roman foot at 11'62 

 English inches, the pace, which was five feet, must have been 58'1 

 inches or 4'84 English feet. 



Here we might have stopped, if it had not been necessary to explain 

 something relative to what it pleased the writers of the middle ages to 

 call the geometrical pace, composed of five geometrical feet. What they 



ARTS AND SCI. D1V. VOL. VI. 



meant by this measure is not easily understood, except by the suppo- 

 sition (which some of their writings confirm) that they imagined a fixed 

 and universal measure of length to exist in nature, and to have been 

 actually obtained. At the beginning of the 16th century the Roman 

 mile, at least the mile of^oOOO feet or 1000 paces, was generally used by 

 writers [MILE], and itinerary measures were more often written about 

 than verified. The stadium, or eighth part of this mile, had also been 

 introduced (into books) from the Greek system, and it was the common 

 opinion, derived from Ptolemy, that the degree of latitude was exactly 

 500 stadia, or 62 J miles. This made the pace, or the 125th part of the 

 stadium, stand forward as a proper universal measure, being the 

 62500th part of that which all believed the degree of latitude to be. 

 But though this may be a probable origin of the geometrical pace, it ia 

 certain that writers did not adhere uniformly to it, so that the later 

 metrologists have formed different notiona of its length. We shall 

 give the accounts of several modern writers. 



Dr. Bernard makes the geometrical pace (which he also calls the 

 land-surveyor's pace) to be five English feet. Greaves supposes that a 

 pace of upwards of 69 inches was once in use in England. O/.anam 

 makes the geometrical pace to be the same as the Roman pace. Eysen- 

 schtnidt does not mention the measure at all. Paucton (who has a 

 theory about the derivation of measures from parts of the human 

 body) makes it only 4 J Roman feet. Rome de L' tele, who contends 

 that Paucton has several times confounded the Greek Olympic foot 

 with the Roman foot, makes it 4J Olympic feet, that is, 4.^ English 

 feet very nearly. An old writer, Samson d'Abbeville, cited by 

 Paucton, lays down the geometrical pace at 5 French feet, and never- 

 theless makes the Roman mile to contain a thousand such paces. The 

 conclusion ia, that the geometrical pace was an invention of the old 

 writers, a needless addition to the confusion in which their accounts 

 of ancient measures were already enveloped. 



There is a pace mentioned in ecclesiastical writers called paasia 

 eccletiaxticui, or dexter (see Uucange, at the word Dextri), which Dr. 

 Bernard, without stating any authority, makes of the same length as 

 the English yard. 



PACKFONG. [GERMAN SILVER.] 



PACKING-PRESS. The hydraulic press invented by Mr. Bramah, 

 besides being used to draw piles, trees, Ac., from the ground, or to 

 prove the strength of materials, is frequently employed to pack or 

 compress bales of linen, cotton, and the like goods into small dimen- 

 sions for the convenience of transport. A description of this machine 

 has been given under HYDRAULIC PRESS ; and it is intended here 

 merely to notice the method employed by Mr. Barlow to determine 

 the thickness which the cylinder should have in order that its strength 

 may be in equilibrio with the strain to which it is subject from the 

 pressure of the fluid within it. 



Within any section of the cylinder made by a plane perpendicular to 

 the axis, the tendency of the contiguous particles of metal to separate 

 from one another in a direction perpendicular to a diameter passing 

 through them, in consequence of the expansion produced by the pres- 

 sure of the fluid, becomes continually less from the interior to the 

 exterior circumference of the section, and is inversely proportional to 

 the distances of the particles from the axis of the cylinder ; and the 

 cohesive power of the particles is, by the laws of elasticity, proportional 

 to their separation, while the strain produced by the pressure of the 

 fluid varies, at any part of the section, with the distance of that part 

 from the axis. It follows that the resistance opposed at such part of a 

 section to the momentum of the pressure is inversely proportional tc 

 the square of the distance from the axis. 



Therefore r representing the radius of the interior surface of th. 

 cylinder, t the whole thickness, and z any variable distance from the 



interior surface towards the exterior, all in inches; then / '' l '' ,if 



J (r + xf 



multiplied by 2 r, and also by the force of cohesion on a square inch 

 of the metal, will express the resistance produced by an annulus which 

 is one inch deep in a direction parallel to the axis. That integral, for 



the whole thickness t, is ; therefore / (in pounds) denoting the 

 Zwrtf 



force of cohesion, 



r + t 



expresses the whole resistance. 



If /' (in pounds) represent the force on a square inch of the interior 

 surface, by which the pressure of the fluid tends to strain the cylinder, 

 2ir?/' will denote the whole strain on the same annulus; therefore, 

 equating the strength and strain, there is obtained 



t - 



t 

 This value of t expresses the required thickness. 



