THE MOST PERFECT PRECISE EEVEE IN THE WORED 



This level was designed and made by the Coast and Geodetic Survey and is recognized 

 by engineers as being superior to every other known make. It can produce more rapid and 

 efficient work for a less cost than any other type. It has been officially adopted not only by 

 the government of the United States, but also by those of India, Mexico, Canada, and Egypt 

 (see page 673). 



We say that it is simply a mechanism 

 that does these things ; but when it is re- 

 membered that the machine has 15,000 

 parts, and that 15 years of careful work 

 were required in its construction, we 

 understand that it is not very simple 

 after all. 



The records made by this machine are 

 used wherever men sail the seas, and as 

 the question of a foot or two in depth 

 on a dangerous shoal may involve the 

 lives and the property on a passing ship, 

 while the commercial prosperity of a port 

 may depend upon information about the 

 tides, this great machine serves more 

 than a theoretical purpose. Its tabula- 

 tions do for the waters what the Amer- 

 ican Ephemeris and Nautical Almanac 

 does for the stars in aiding navigators. 



THE WONDER OE THE TIDES 



The tides are among the most remark- 

 able phenomena in the world of nature, 



and they give rise to many peculiar no- 

 tions concerning the level of the oceans. 

 The tide at Panama, for instance, rises 

 much higher than the tide at Colon, and 

 this leads many people to think that the 

 Pacific has a higher level than the At- 

 lantic. As a matter of fact, however, 

 while the tidal fluctuations on the Atlan- 

 tic side have a range about 2 feet and 

 those on the Pacific side a range of about 

 20 feet, the level of the oceans is the 

 same. The difference is caused by the 

 narrowing shoreline of Panama Bay, 

 which takes a broad expanse of water as 

 it enters the bay and narrows it down as 

 it sweeps into the V-shaped entrance. 

 What it loses in breadth it must make up 

 in depth, and hence the higher tides on 

 the Pacific side of the Isthmus at 

 Panama. 



The same phenomenon is witnessed in 

 the Bay of Fundy, where at the head of 



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