SOME REFINEMENTS OF MECHANICAL SCIENCE. 145 



A clock in the observatory at Berlin has run for several months 

 under these favoral)le conditions with a rate having a mean error 

 of but fifteen one-thousandths of a second per day and a nuiximum 

 error of thirty one-thousandths of a second per day. 



Another clock, installed at the observatory of Case School of Ap- 

 plied Science, at Cleveland, running under similar conditions, also 

 has a mean error of fifteen one-thousandths of a second i)er day, with 

 a maximum error for several months of but twenty-two one-thou- 

 sandths of a second per day. 



These are notable examples of the present state of the art of clock 

 making and show the wonderful precision with which minute inter- 

 vals of time can be measured. 



From the time of the invention of Peter Ilele, in 1477, of the 

 " Nureml)urg animated egg,'' or '' pocket clock," wdiich required 

 winding twice a day and varied an hour and a half in the same length 

 of time, the development of the watch has kept pace with the 

 " mother clock " and followed closely to it in time-keeping qualities. 



These marvelous little machines, whether made at the homes of the 

 peasants among the hills and mountains of Switzerland, where the 

 skill required for nudging a single part has been handed <lown from 

 generation to generation, or made in the great factories of this coun- 

 try, where fully 2,000,000 high-grade movements are turned out 

 annually and where the skill of the workmen has been supplemented 

 by modern methods and machinery, are, notwithstanding the difficul- 

 ties attending their manufacture, jjroduced so cheaply as to be within 

 the reach of almost everyone. 



The larger watch, or ship chrono]neter, with its escapement so 

 delicately made and adjusted that it must always be kept in the 

 same position, was greatly improved through the efl'orts of the Brit- 

 ish Government in 1714 by offering rewards of ten, fifteen, and twenty 

 thousand pounds to any who should make chronometers that would 

 run so accurately that the longitude of a ship at sea could be deter- 

 mined Avithin CO, 40, and 30 miles. Harrison, the inventor of the 

 compensating pendulum and the compensating balance, which is now 

 used in watches, succeeded in making a chi'onometer which, after 

 being tested on a long voyage, was found to run so closely that the 

 position of the ship was determined within 18 miles, and he was 

 therefore paid the full award of £20,000. That historic chronometer, 

 which marked a new era in navigation, is now numbered among the 

 treasures of the Greenwich Observatory. 



Modern ships are equipped with chronometers so accurate and so 

 reliable and with sextants of such precision that navigators can 

 determine their position in latitude and longitude within a few miles. 

 Therefore, with the increased speed of the powerful shij)s, carrying 

 hundreds or even thousands of passengers, together with their val- 



