CLOCK 



1436 



CLOCK 



minute, hand with it. Wheel E is made to 

 move by touching wheel F. At the back of 

 wheel E is another smaller wheel with only 

 six teeth ; these fit into teeth in wheel B, which 

 has seventy-two teeth, and carries the hour 

 hand. Turning the small wheel of six teeth 

 causes the large wheel B, with its seventy-two 

 teeth, to turn just one-twelfth of the way 

 round. Thus the combination of wheels causes 

 F to turn twelve times while B turns but once. 



Modern Spring Clocks. Though for centuries 

 pendulums and weights were used, requiring 

 perfect equilibrium and permitting only an 

 upright position, it was eventually discovered 

 that clocks could be made without them and 

 that a small steel spring would perform the 

 same office. Instead of having a pendulum, 

 spring clocks are fitted with a balance wheel, 

 which prevents the other wheels from turning 

 too rapidly. Small clocks and watches are 

 made on the same principle, and both were 

 impossible before the adoption of the spring; 

 all that is necessary to start the mechanism 

 is to wind, or tighten, the spring. 



Striking Clocks. Naturally when clocks 

 were perfected and the time could be seen 

 by anyone at a glance, the idea of a clock 



NEW FORM OF DIAL, 



The inner circle of figures represents the 

 hours ; the outer circle, the minutes of the hour. 

 This dial is especially valuable in railway sta- 

 tions. 



which would announce the hours so that all 

 in the vicinity could hear was evolved. The 

 striking mechanism is separate from the or- 

 dinary time-keeping machinery. A weight or 

 spring sets in motion wheels which release a 

 hammer at Certain times. The hammer falls 

 on a bell or rod of metal and announces the 



hour. Many clocks have elaborate devic 

 for striking chimes on a series of bells, fc 

 playing tunes and for making certain figur 

 go through regulated motions at regular inter 

 vals. One .of the most interesting and compli- 

 cated of clocks is to be seen in Strassburg 

 Cathedral in Germany. Many clocks, instead 

 of striking the hours, have an attachment 

 which causes a bell to ring at a certain time. 

 These are called "alarm clocks," and are in 

 great demand among those whose business 

 demands early rising. 



Electric Clocks. The most important appli- 

 cation of electrical knowledge to clock-making 

 is the operation of a number of clocks in differ- 

 ent places in unison with a master clock in an 

 observatory, but there are also electric clocks 

 which differ from 

 the ordinary 

 clock chiefly in 

 deriving power 

 from batteries in- 

 stead of from 

 weights or 

 springs. The pic- 

 ture shows one 

 method of oper- 

 ating either type 

 of clock. The 

 cylinder a is an 

 electro-magnet in 

 which the current is alternately excited and 

 broken by the swinging of a pendulum, which 

 in the case of a series of clocks is that of the 

 master clock. When current passes through 

 the coil the lower end of the armature lever 

 b is attracted and the pawl c pulled back as 

 the lever swings on its pivot. The back-stop / 

 prevents the ratchet wheel d from slipping. 

 When the current is broken the spring e draws 

 the lever back and the wheel receives a push. 



Clock-Making Industry. So great is the 

 demand for clocks that the United States alone, 

 besides providing for nearly all its own needs, 

 exports them to the value of $3,000,000 an- 

 nually. American enterprise, to which is due 

 the introduction of the cheap but efficient 

 steel spring, has revolutionized clock-making 

 throughout the world. For more than 200 

 years previously coiled springs had been used 

 by European clock makers, but only in the 

 most expensive clocks. Now the spring clocks 

 made in the United States are the cheapest, 

 and in proportion to their cost, the most 

 satisfactory that can be obtained. Fairly re- 

 liable clocks can be purchased for one dollar, 



