PRO 



PRO 



Cor. 2. Let A H = H P, and it will be 

 L X C N = A H q. L x N H, whence 

 it will be N H = C N ; and consequently 

 the right line A F, being the line of direc- 

 tion of the projectile, will be a tangent to 

 the parabola. 



Cor. 3. If a heavy body be projected 

 downwards, in a direction oblique to the 

 horizon ; the path of the projectile will be 

 a parabola. 



Theorem 3. The impetus of a projected 

 body in different parts of the parabola, are 

 as the portions of the tangents intercept- 

 ed between two right lines parallel to the 

 axis ; that is, the impetus of the body 

 projected in the points A and B (fig 1 . 9) to 

 which A D, and B E are tangents, will be 

 as C D and E B, the portions of the tan- 

 gents intercepted between two right lines 

 C B, and UE parallel to the axis. 



We have here treated the path of a pror 

 jected body as an exact parabola, though, 

 from the resistance of the air, the line of 

 a projectile is not exactly parabolical, but 

 rather a kind of hyperbola; which, if con- 

 sidered and applied to practice, would 

 render the computations far more operose, 

 and the very small difference (as experi- 

 ence shows in heavy shot) would, in a 

 great measure, lessen the elegancy of the 

 demonstrations given by accounting for 

 it ; since the common rules are sufficient? 

 ly exact, and easy for practice. 



PROJECTION, in mechanics, the art 

 of communicating motion to a body, from 

 thence called projectile. In perspective, 

 projection is the appearance or represen- 

 tation of an object on the perspective 

 plane. The projection of the sphere is 

 either orthographic, or stereographic. 

 The former, or orthographic, projection 

 supposes the eye placed at an infinite dis- 

 tance ; whereas, in the stereographic pro- 

 jection, it is supposed to be only 90 de- 

 grees distant from the primitive circle, or 

 placed in its pole, and thence view- 

 ing the circles on the sphere. The pri- 

 mitive circle is that great circle which 

 limits or bounds the representation or 

 projection ; and the place of the eye is 

 called the projecting- point. 



PROLATE, in geometry, an epithet ap- 

 plied to a spheroid, produced by the re- 

 volution of a semi-ellipsis about its larger 

 diameter. 



PROLEGOMENA, in philology, certain 

 preparatory observations or discourses 

 prefixed to a book, &c- containing some- 

 thing necessary for the reader to be ap- 

 prized ot, to enable him the better to un- 

 derstand the book, or to enter deeper into 

 the science, &c. 



PROMISE, in law, is where, upon a 

 valuable consideration, persons bind them- 

 selves by words to do or perform such a 

 thing agreed on : it is in the nature of a 

 verbal covenant, asd wants only the so- 

 lemnity of writing and sealing to make it 

 absolutely the same. Yet, for the breach 

 of it the remedy is different ; for, instead 

 of an action of covenant, there lies only 

 an action upon the case, the damages 

 whereof are to be estimated and deter- 

 mined by the jury. If there is no consi- 

 deration, it is void, and it is culled a nude 

 compact, or, in Latin a nudum pactum. 



PROMISSORY note. See BILLS of 

 Exchange. 



PRONOUN, pronomen, in grammar, a 

 declinable part of speech, which, being 

 put instead of a noun, points out some 

 person or thing. See GRAMMAR. 



PRONUNCIATION, in grammar, the 

 manner of articulating or sounding the 

 words of a language. Pronunciation 

 makes much the most difficult part of a 

 written grammar; in regard that a book 

 expressing itself to the eyes, in a matter 

 that wholly concerns the ears, seems next 

 akin to that of teaching the blind to dis- 

 tinguish colours ; hence it is, that there is 

 no part so defective in grammar as that of 

 the pronunciation, as the writer has fre- 

 quently no term whereby to give the rea- 

 der an idea of the sound he would ex- 

 press ; for want of a proper term, there- 

 fore he substitutes a vicious and preca- 

 rious one. To give a just idea of the pro- 

 nunciation of a language, it seems neces- 

 sary to fix as nearly as possible all the se- 

 veral sounds employed in the pronuncia- 

 tion of that language, 



PRONUNCIATION is also used for the 

 fifth and last part of rhetoric, which con- 

 sists in varying and regulating the voice 

 agreeably to the matter and words, so as 

 most effectually to persuade and touch 

 the hearers. It is much the same with 

 what is otherwise called emphasis. 



This emphasis is a considerable stress 

 or force of voice, laid upon that word in 

 a sentence by which the sense of the 

 whole is regulated: thus, suppose you 

 were asked, " are you determined to walk 

 this day to London ?" If the emphasis be 

 placed on the word you, the answer may 

 be, " yes, I go myself;" or, " no, I shall 

 send my son." Again, if it be placed on 

 the word -walk, the answer is, " yes, I 

 am ;" or, no, I shall ride :" if on the 

 words to-day, then the answer is, " yes ;" 

 or, " no, I shall go to-morrow :" and 9 

 lastly, if the emphasis be placed on the 



