HYDROGRAPHICAL NOTES. 
165 
of an inch thick, and separated about an inch from the fifth 
case by a column of water. The size of the machine alto- 
gether was about two feet high, and ten inches in diameter. 
To the bottom of the machine was fastened a weight of 7^ 
pounds, and to the upper part the end of a coil of two-inch 
rope. I first veered 779 fathoms of two-inch rope over- 
board, then 390 fathoms of two and a half, then S66 fa- 
thoms of three-inch, making in all 1435 fathoms of rope. 
I had attached a thirtj-two-pound shot to every 200 
fathoms. It took twenty-two minutes to veer the whole 
overboard ; and the apparatus was allowed to remain, after 
the whole was veered out, twelve minutes, before we com- 
menced hauling it in, that the whole might have time to 
sink. From the great friction, we found much difficulty in 
getting it on board again ; it took a hundred men just one 
hour and twenty minutes to do so. The thermometer, 
when it came up, stood at 42°, and the temperature of 
the surface-water was 73°, making a difference of 31°. 
I should imagine that the thermometer here had sunk 
about 1000 fathoms : the line did not go down perpendi- 
cularly. I determined the perpendicular depth by taking 
the angle which the line made with the ship's bow, and 
calling the line veered out the hypothenuse of a right- 
angled triangle, (which would not be quite correct). I 
thus found the perpendicular depth to be 1100 fathoms: 
but as the line would form a curve, I think the perpendi- 
cular depth would be as near as possible about 1000 fa- 
thoms. A little breeze sprung up towards the end of our 
operations, and the ship rode to the sunk line precisely as 
if she had been at anchor. — This experiment was made on 
the coast of Africa, in Lat. 3° m S., Long. 7° 59' E, 
