HYDROGRAPHtCAL SURVEY. 20S 



come buoyant, after being a few hours relieved from 

 pressure, though kept constantly under water ; but 

 all other kinds of wood yet tried, though they lose a 

 little of their moisture, yet remain specifically heavier 

 than water, as long as they are kept immersed . Blocks 

 of wood, indeed, are now in my possession, that were 

 soaked with sea- water in the year 1817, and yet re- 

 main, at the bottom of a vessel of water, nearly as 

 heavy as when first drawn up out of the sea. 



The degree of pressure at the depth to which I 

 sounded in my last experiment, is not a little asto- 

 nishing, being, under a column of water, 6348 feet 

 in length, at least, 2823 lb. or 25 civt. 23 Ih. on 

 one square inch of surface *. Hence on the larger 

 cubes of ash used in the experiment, though mea- 

 suring only 1.59 inches in diameter, the whole pres- 

 sure must have exceeded nineteen tons ! 



SECT. III. 



Remm^ks on the Currents of the Arctic Sea, zvith 

 Observations respecting Waves. 



The determination of the various horizontal mo- 

 tions in the great body of waters of the ocean, is a 



* In tliis calculation, as well as others of the same nature, 

 the weight of the column of sea-water is taken throughout^ the 

 same as at the surface, where a cubic inch, temperature SO", 

 weighs 259.58 grains. As, however, water is found to b^ 

 somev/hat compressible, its weight, at great depths, must be 

 greater than at the surface ; and consequently the whole pres- 

 sure on the specimens of v/ood, greater than in the above esti-* 

 nation. 



