HYDROGRAPHICAL SURVEY. 197 



measuring depths from a vessel, when saiUng slow- 

 ly, or drifting through the water, cease to be useful 

 beyond 200 or 300 fathoms*. With this view, I not 

 only attached pieces of wood of different kinds, to 

 the lead, and provided counterparts for immersion 

 in a bucket of water ; but I also fastened cubes of 

 ash, from the same piece of timber, of about one 

 inch solid contents, and of the same exact weight, 

 to the line, at intervals of about 500 feet ; by the 

 weight of which, when taken up, I could ascertain 

 whether the increase of specific gravity was in any 

 way proportionate to the depth. AVhen the speci- 

 mens of wood for this experiment were procured, a 

 clear grained piece, of double the size wanted for 

 sending under water, was prepared, and then cut in 

 two, and the two parts dressed to the same shape, 

 and to within a quarter of a grain of the same 

 weight : one of these was then adopted as a princi- 

 pal, and fixed to the lead or line ; and the other as 

 a counterpart, and put into a bucket of water. 

 The specimens affixed to the lead were eleven in 

 number, and consisted of wood of different kinds, 

 shapes, and dimensions : they were sunk to the 



* A veiy recent contrivance, for obtaining soundings from 

 a vessel vinder-way, founded on the small change in bulk which 

 takes place in water when strongly compressed, promises to 

 answer the design at still greater depths than 200 or 300 fa- 

 thoms. 



