PENDULUM 



PENETANGUISHENE 



half the arc is known as the amplitude oj oscil- 

 lation. In Fig. 1, b d is the arc through which 

 the weight c swings, and 6 a c is the amplitude 

 of oscillation. A pendulum about 39.1 inches 

 long will vibrate once each second in the lati- 

 tude of New York. The shorter the pendulum 

 the more frequent are the vibrations, if the 

 amplitude remains the same. 



There are four laws of the pendulum, stated as 

 follows : 



i 1 > The time of vibration Is Independent of the 



mass. 



In the same pendulum, all vibrations of 

 amplitude are made In the same time. 

 (3) The time of vibration varies directly as 

 the square root of the length. A pendulum one- 

 ninth the length of another will vibrate three 

 times as fast. 



The time of vibration varies inversely as 

 the square root of the acceleration, or force of 

 gravity. 



In general, the time of vibration decreases as 

 the pendulum is moved from the equator toward 

 either pole. 



The simple, or ideal, pendulum, a weight 

 suspended from a thread (shown in a, Fig. 2), 

 could not be used for a clock, because the 

 thread would not be stiff enough to set in mo- 

 tion other portions of the mechanism. A prac- 



tical pendulum, therefore, is usually of the 

 form shown in 6, Fig. 2; it consist* of a flat- 

 tened bob supported by a rod, with a screw be- 

 neath the bob to adjust the length of the pen- 

 dulum. The pendulum is lengthened when the 

 clock runs too fast, and shortened when it run- 

 too slow. 



Since the rod in a clock pendulum tends to 

 expand in summer and shorten in winter, clocks 

 known as regulators are supplied with so-called 

 gridiron pendulums, consisting of several brass 

 and steel rods so attached that some expand 

 upwards and some downwards, thus keeping the 

 mean length constant (see c, Fig. 2) . In another 

 device the length is kept constant by the ex- 

 pansion and contraction of mercury in a cup 

 which swings at the end of the rod, in place 

 of the ordinary weight. See CLOCK. 



PENELOPE, penel'opc, a Grecian princess 

 who, according to the old myth, became the 

 wife of Ulysses about the same time that Helen. 

 her cousin, was married to Menelaus. Soon 

 after the birth of Telemachus, Ulysses left Pe- 

 nelope to go with the Greeks to the Trojan 

 War. For twenty years he did not return, and 

 during this long absence Penelope was perse- 

 cuted by aspiring and persistent suitors, who 

 endeavored to convince her that the long ab- 

 sence of her husband meant his death. She 

 succeeded in keeping them at a distance and in 

 deferring her decision, telling them that as soon 

 as she had completed a web which she was 

 weaving she would give them an answer; but 

 < ich night she unraveled what she had woven 

 during the day. After a time, however, she was 

 detected in this and driven to make a decision. 

 Accordingly, she promised to mam- him who 

 could bend and ui -fully the massive 



bow of Ulysses. All tried and failed excepting 

 a beggar who had come into the hall among 

 the spectators. This man succeeded with little 

 apparent effort, and was then recognized as 

 Ulysses himself, who had just returned to his 

 kingdom. The hero then turned his arrows 

 upon the troublesome suitors and slew them 

 one after another. 



The reader is referred to 

 the following articles in these volumes: 



Helen of Troy Troy 



'.ins 



PENETANGUISHENE, /, n . t an' gisk een' , 

 a town in Simcoe County, Ontario, at the 

 southeastern end of Georgian Bay, on the 

 id Trunk Railway, 102 miles north of To- 

 ronto, thirty-six miles northwest of Orillia and 

 thirty-eight miles north of Barric. Pcnetan- 

 guishenc is the mecca of thousands of American 

 and Canadian tourists who make annual pil- 

 grimages to Georgian Bay in search of health 

 and pleasure. It has a deep yet snug harbor 

 which is surrounded by beautiful hills. Its 

 name is an Indian word, meaning "white, roll- 

 ing sand/' which tells the story of its attrn- 



