THE CONQUEST OF TIME AND SPACE 



From the standpoint of practical navigation the dip of 

 the needle is a matter of much less significance than its 

 horizontal fluctuations. Robert Norman himself at- 

 tempted to overcome the dip by a balancing apparatus 

 applied to the needle; and the modem compass is 

 suspended in such a way that the propensity to dip does 

 not interfere with the lateral movements which supply 

 the navigator with all important information. The 

 modem compass in question is the invention of Lord 

 Kelvin and was patented by him in 1876. It consists 

 of a number of small magnets arranged in parallel and 

 held in position by silk threads, each suspended, cob- 

 web-like, from the circular rim of aluminum. The 

 weight — which in the aggregate is relatively slight — 

 being thus largely at the circumference, the instmment 

 has a maximum period of oscillation and hence a high 

 degree of stability. Its fluctuations due to the ship^s 

 influence are corrected by a carefully adjusted disposi- 

 tion of metal balls and magnets. 



SAILING BY DEAD RECKONING 



While the compass gives indispensable information as 

 to direction, and is constantly under the eye of the pilot, 

 it of course can give no direct information as to the 

 distance traversed by the ship, and hence does not by 

 itself suffice to tell the navigator his whereabouts. In 

 the early days there was indeed an expectation that 

 the observed declination of the compass would reveal 

 to the navigator his longitude and that the observation of 

 the dip might enable him to determine his latitude. 



[14] 



