F. GEOGRAPHY. 243 



opinion that for the future improvement in the health of pa- 

 tients will depend more upon visiting and dwelling for a suit- 

 able length of time on high altitudes than to any resort to 

 the low lands of the sea-shore, which has hitherto been so 

 much in vogue. 



THE THEORY OF THE USES OF THE SURVEYOR^ LEVEL. 



Professor Wittstein states that if one imagine a leveling 



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to be conducted along the ocean level from the pole of the 

 earth to some point on the equator, then, in consequence of 

 the method according to which the level is ordinarily used, 

 the value of the difference in altitude of the two ends of the 

 given line would be exactly zero. To this Helmert adds that 

 the conclusion can only be correct when we neglect the un- 

 equal curvature of the various points of the level surface as 

 we proceed from the pole to the equator, since Wittstein's 

 conclusion certainly involves the assumption that the level 

 or horizontal plane is tangent to a perfectly spherical surface. 

 Oudemans, of Batavia, has taken up the question at this point, 

 and investigates the amount of the accumulated error that 



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would result from the assumption which Helmert has correct- 

 ly shown to be involved in Wittstein's statement. He con- 

 cludes that, if the average distance between two successive 

 stations in the course of the leveling operation be 600 feet, 

 then the sum of all the possible errors arising from this source 

 a v i 1 1 amount to only one five-thousandth part of an inch in the 

 entire quadrant of the earth's circumference, but will amount 

 to three feet if the average distance between the successive 

 stations be so great as twenty miles. In either case the error 

 would be inappreciable in comparison with those arising from 

 other causes. Astron. JVachric/ite?7, LXXXIIL, 23. 



SAILING DIRECTIONS FOR ATLANTIC NAVIGATION. 



No. 45 of the publications of the United States Hydro- 

 graphic Office, of the Bureau of Navigation, is an elaborate 

 memoir on the navigation of the Atlantic Ocean, translated 

 bv Lieutenant-Commander Coghlan from the French of Mons. 



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F. Labrosse. The volume is devoted, first, to a general ac- 

 count of the calms, winds, currents, icebergs, and barometric 

 pressures ; and, second, to the different routes from various 

 parts of the world to other portions of these coasts ; and is 



