F. GEOGRAPHY. 233 



greater portion of the remaining bottom surface of the basin 

 a thin layer of mercury, possibly the one hundredth of an 

 inch deep, which will not be troubled by the ripples that 

 originate near the edges of the basin. It is easy, he says, by 

 gentle taps upon the trough, to observe these ripples starting 

 from the edge, but quickly dying out as they come upon the 

 plateau where the mercury is relatively shoal. It might be 

 anticipated that a slight inclination of the basin would mate- 

 rially alter the horizontality of the surface of the mercury. 

 He states, however, that this is not the case to any injurious 

 extent, the momentary tilting of the mercurial surface being 

 immediately followed by a resumption of its horizontality. 

 Mr. Lane's arrangement for procuring a thin, steady horizon- 

 tal mercurial film seems to be an improvement upon that 

 proposed many years ago by Lamont, and will doubtless be 

 found exceedingly convenient in many astronomical observa- 

 tions, if it be not injuriously aftected by inequalities of tem- 

 perature, as Lamont showed was the case in his own appara- 

 tus. Coast Survey Report^ 1871, 189. 



CORRECTION OF ASSUMED ALTITUDES IN THE UNITED STATES. 



Mr. James T. Gardner, the Geographer of the United States 

 Geological and Geographical Survey of the Territories under 

 Professor F. V. Hayden, has published an elaborate discussion 

 of the evidence upon wiiich rested the supposed altitudes of 

 leading points in the Northern and Western United States, 

 our great lakes, rivers, cities, mountains, etc. He had before 

 him a collection of over 1200 railroad and canal profiles, and 

 among this mass were many conflicting statements. Cor- 

 rected profiles were joined together into various lines ex- 

 tending from ocean tide-gauges to the interior of the coun- 

 try. These lines focusing at great railway centres, gave 

 the means of determining the altitude of each of them by a 

 number of independent methods. Diflerent results accord so 

 closely, and evidence is given with such completeness, that 

 Mr. Gardner's work must be considered to have established 

 the altitudes of the LTnited States. The heioht of the mean 

 surface of Lake Erie is shown to be 573.08 feet, and of Lake 

 Michigan, 589.15 feet above the sea. Tliis difiers considera- 

 bly from former results, and Mr. Gardner points out the old 



