OF TIDE'S. 34$ 



$t. Pierre in corroboration of the demonstration I have just noticed ; 

 but, as I conceive myself to have fully disproved the geometrical 

 evidence, I shall not trouble you with an attempt to invalidate these 

 subsidiary confirmations. 



The second proof (says he) is atmospherical. It is well known 

 that, in proportion as you ascend a mountain, the mercury in the 

 barometer subsides : now the mercury sinks in the barometer in 

 proportion as you advance northward. The weight of one line of 

 mercury at Paris is equivalent to an elevation of 10 fathom and 5 

 feet, whereas in Sweden it is equivalent to 10 fathom 1 foot 6 inches 

 only ; and of course the ground of Sweden must be higher. From 

 a series of observations made by Captain Cook in the southern 

 hemisphere in 1773 to 1775, we perceive the mercury scarcely ever 

 rises higher than 29 inches beyond the 60th degree of south lati- 

 tude, and mounted almost always to 30 inches and even higher in 

 the vicinity of the torrid zonej which proves that the barometer 

 falls as you recede from the line, and that both poles are elongated. 



The third proof it nautical, arising from the annual descent of 

 the ices toward the line, impelled by currents proceeding alter, 

 tiately from each pole during their respective summers, immense 

 mountains of ice being frequently seen by navigators in low lati- 

 tudes. 



The fourth proof is astronomical. Childrey (an English author of 

 note) supposes, says M.St. Pierre, that the earth at the poles is covered 

 with ice to such a height as to render its figure sensibly oval. Kep- 

 ler says that the eclipse of the moon on the 26*th September 1624, 

 like the one observed by Tycho Brahfe in 1588, which was total, 

 and very nearly central, differed widely from the calculation : for, 

 not only the duration of total darkness was extremely short, but 

 the rest of the duration, previous and posterior to the total obscura- 

 tion, was still shorter, as if the figure of the earth was elliptical, 

 having the smallest diameter under the equator, and the greater 

 from pole to pole* 



Navigators in the north have always seen the elevation of the sun 

 above the horizon greater the nearer they approach the poles. It 

 is impossible to ascribe these optical effects to atmospherical refrac- 

 tion. 



Barents, on the 24th of January, in Nova Zembla, saw the sun 

 15 days sooner than he expected, which would give a refraction of 



z3 



