PEN 



PEN 



also annexed to secure the performance 

 of certain covenants in a deed, articles of 

 agreement, copartnership, &c. In a bond 

 also for payment of money, it is usual to 

 annex a penalty in double the amount of 

 the obligation. See BOND. 



PENCIL, an instrument used by pain- 

 ters for laying- on their colours. Pencils 

 are of various kinds, and made of various 

 materials ; the larger sorts are made of 

 boars bristles, the thick ends of which 

 are bound to a stick, bigger or less, ac- 

 cording 1 to the uses they are designed for; 

 these, when large, are called brushes. 

 The finer sorts of pencils are made of 

 camels, bad ers, and squirrels-hair, and 

 of the down of swans ; these are tied at 

 the upper end with a piece of strong 1 

 thread, and inclosed in the barrel of a 

 quill. All good pencils on being 1 drawn 

 between the Jips come to a fine point. 



PENCIL is also an instrument used in 

 drawing 1 , writing 1 , &c.-made of long- pieces 

 of black lead, or red-chalk, placed in a 

 groove cut in a slip of cedar, on which 

 other pieces of cedar being glued, the 

 whole is planed round, and one of the 

 ends being cut to a point, it is fit for use. 



PENDANT, an ornament hanging at 

 the ear, frequently consisting of diamonds, 

 pearls, and other precious stones. 



PENDANTS, in heraldry, parts hanging 

 down from the label, to the number of 

 three, four, five, or six at most, resem- 

 bling the drops in the Doric frieze. When 

 they are more than three, they must be 

 specified in blazoning. 



PENDANTS, of a ship, are those stream- 

 ers or long colours which are split and 

 divided into two parts ending in points, 

 and hung at the head of masts, or at the 

 yard-arm ends. 



PENDULOUS, a term applied to 

 any thing that bends or hangs down- 

 wards ; thus, the flowers, whose slender 

 stalks are not able to sustain their heads 

 upright, are called pendulous flowers. See 

 BOTANY and FLOWER. 



PENDULUM, in mechanics, denotes 

 any heavy body, so suspended as that it 

 may vibrate or swing backwards and for- 

 wards, about some fixed point, by the 

 force of gravity. The vibrations of a 

 pendulum are called its oscillations. See 

 OSCILLATION. A pendulum, therefore, 

 is any body, B, (Plate XII. Miscell. fig. 

 8), suspended upon, and moving about, 

 a fixed point, A, as a centre. The na- 

 ture of a pendulum consists in the follow- 

 ing particulars : 1. The times of the vi- 

 brations of a pendulum, in very small 



arches, are all equal. 2. The velocity of 

 the bob, in the lowest point, will be near- 

 ly as the length of the chord uf the arch 

 which it describes in the descent. 3. The 

 times of vibration in different pendulums, 

 A B, A C, are as the square roots of the 

 times of their vibrations. 4. The time 

 of one vibration is to the time of the de- 

 scent, through half the length of the pen- 

 dulum, as the circumference of a circle 

 to its diameter. 5. Whence the length 

 of a pendulum, vibrating seconds, will 

 be found 39.2 inches nearly ; and that of 

 an half second pendulum 9.8 inches. 

 6. An uniform homogeneous body B G 

 (fig. 9) has a rod, staff', &c. which is 

 one-third part longer than a pendulum 

 A I), will vibrate in the same time with 

 it. 



From these properties of the pendu- 

 lum we may discern its use as an univer- 

 sal chronometer, or regulator of time, as 

 it is used in clocks, and such-like ma- 

 chines. See CHRONOMETER, HOIIOLOGY, 

 &c. 



By this instrument also we can mea- 

 sure the distance of a ship, by measuring 

 the interval of time between the fire and 

 the sound of the gun ; also the distance of 

 a cloud, by numbering the seconds, or 

 half-seconds, between the lightning and 

 thunder. Thus, suppose between the 

 lightning and thunder, we number 10 

 seconds ; then, because sound passes 

 through 1142 feet in one second, we have 

 the distance of the cloud equal to 11420 

 feet. Again, the height of any room, or 

 other object, maybe measured by a pen- 

 dulum vibrating from the top thereof. 

 Thus, suppose a pendulum from the 

 height of a room vibrates once in three 

 seconds ; then say, as 1 is to the square 

 of 3, viz. 9, so is 39.2 to 352.8 feet, the 

 height required. Lastly, by the pen- 

 dulum we discover the different force of 

 gravity on different parts of the earth's 

 surface, and thence the true figure of 

 the earth. 



When pendulums were first applied to 

 clocks, they were made very short ; and, 

 the ai-cb.es of the circle being large, the 

 time of vibration through different arches 

 could not in that case be equal ; to effect 

 which, the pendulum was contrived to 

 vibrate in the arch of a cycloid, by mak- 

 ing it play between two semi-cycloids C 

 B, C D (fig. 10), whereby it describes 

 the cycloid BEAD; the property of 

 which curve is, that a body vibrating in 

 it will describe all its arches, great or 

 small, in equal times. These are, how- 

 ever, which concur in rendering the ap- 



