CENTRIPETAL FORCE 



1255 



CERBERUS 



results is called centrifugal force, a name which 

 means flying from the center. The tendency 

 of every body in motion is to move in a 

 straight line, and this tendency causes the de- 

 velopment of centrifugal force in bodies moving 

 in a circular or curved path. (See CENTRIPETAL 

 FORCE.) 



CENTRIPETAL , sen trip 'etal, FORCE . This 

 is the force which counteracts centrifugal force 

 (see above). In the wheel and the grindstone 

 it is the force of cohesion (which see) that 

 keeps these bodies from flying to pieces and 

 their fragments from scattering in straight lines. 

 In case of the pail of water it is the string. 

 Should the string break or should a person 

 lose his grip on it the pail would fly off in a 

 straight line, but it would soon change its 

 direction owing to the force of gravity, and 

 come to the earth in a curved path. Gravity 

 is the great centripetal force of the earth. Were 

 it not for this, the rapid rotation of our planet 

 as the equator is approached would cause all 

 bodies on its surface to fly, off into space in 

 straight lines. 



CENTURY PLANT, or AGAVE, a gay ' ve, an 

 interesting plant of the deserts, belonging to 

 the aloe family, now often cultivated as a 

 decorative house or garden plant. These plants 

 are generally large, and have a massive tuft 

 of fleshy, spiny-edged leaves, sometimes striped 

 or margined. They live for many years ten 

 to seventy before flowering. This long delay 

 gives them the common name of century plant, 

 although it is misleading. Because of its name 

 many people believe it lives much longer than 

 a century and blossoms but once in a hundred 

 years. When the time for flowering ap- 

 proaches, a tall stem springs from the center 

 of the tuft of leaves and grows very rapidly 

 until it reaches a height of fifteen, twenty or 

 even forty feet, and bears, toward the end, a 

 large number of flowers. Then the leaves, 

 having given their store of nourishment to 

 the production of this large stalk and its 

 flowers droop and die, but the roots soon 

 send up new shoots for the new generation. 



The sap of some of the aloes, when fer- 

 mented, yields an intoxicating beverage resem- 

 bling cider, called by the Mexicans pulque. 

 From others is produced the familiar mescal, 

 another intoxicating drink of the Mexicans. 

 The leaves are used as fodder, and their fibers 

 are also formed into thread, cord and ropes. 

 An extract from the leaves is used as a substi- 

 tute for soap. Slices of the withered flower- 

 stem are used as razor-strops. 



CEPHALOPODA, sef a lop ' o dah, the name 

 of a class of mollusks which includes the 

 cuttlefish, the octopus, the pearly nautilus and 

 the squid, all of which are described under 

 their titles. The name means hcad-jooted, 

 and is given these animals because they have 

 a number of arms, or feet, around the mouth. 

 The arms usually have little cups, or "suckers," 

 on the under side, which enable the animal to 

 fasten itself securely to its prey. 



THE CENTURY PLANT 



CERAMIC, seram'ik, ART. See POTTERY. 



CERBERUS, sur'bcruc, in Greek and Ro- 

 man myths, Pluto's three-headed dog, the grim 

 guardian of the entrance to the underworld. 

 His jaws dripped with foam, from which sprang 

 the deadly nightshade (see NIGHTSHADE) . Early 

 and late he kept his watch, allowing no living 

 being to enter the gates of Hades, nor any 

 spirit to pass out of them. Orpheus, however, 



