THE CONQUEST OF THE ZONES 



tion of one thirty-two-thousandth of an inch as deter- 

 mined by a delicate spirit level. Even when all but 

 absolute decision has been obtained, however, it is 

 quite impossible to maintain it, as the slightest varia- 

 tion of temperature — due perhaps to the application of 

 the hand to one of the pillars on which the trunnions 

 rest — ^may disturb the precise direction of the spider 

 webs and so miUtate against absolute accuracy of 

 observation. The instrument must, therefore, be 

 constantly tested and its exact range of errors noted 

 and allowed for. 



To devote so much labor to details, merely in the 

 eflFort to determine the precise moment at which a star 

 or planet crosses the meridian, would seem to be an 

 absurd magnification of trifles. But when we reflect 

 that the prime object of such observations is to supply 

 practical data which will be of service in enabling navi- 

 gators on all the seas of the globe to bring their ships 

 safely to port, the matter takes on quite another aspect. 

 We have here, obviously, another and a very striking 

 niustration of the close relationship that obtains be- 

 tween the work of the theoretical devotee of science 

 and that of the practical man of affairs. 



SOUNDINGS AND CHARTS 



Though the navigator, thanks to his compass, sex- 

 tant, and Nautical Almanac, may determine with a high 

 degree of precision his exact location, yet even the best 

 observations do not enable him to approach a coast 

 without safeguarding his ship by the use of another 



[41] 



