6o THE POPULAR SCIENCE MONTHLY. 



red, and blue bunting, and knots. The lead is a long, finely-tempered 

 block, generally weighing fourteen pounds, which has a recess at the 

 thick end, and is perforated at the other end for the reception of the 

 line. This instrument is chiefly used while the vessel is in motion. 

 The leadsman swings the lead vigorously, so as to give it momentum 

 enough to carry it well in advance of the ship before it touches the 

 water. It sinks rapidly while the leadsman's position is advancing to 

 the spot where it touched the water. The depth is ascertained by 

 looking at the marks on the line. This method is effective and cor- 

 rect enough for ordinary purposes, in depths of not more than twelve 

 or fifteen fathoms. Accurate soundings may be obtained by reducing 

 the speed of the vessel as much as possible, in depths which do not 

 much exceed thirty or forty fathoms. In ocean-water, where depths 

 of two or three thousand fathoms are met, the vessel must be kept 

 stationary, and heavier weights than are found sufiicient for shallow 

 soundings must be employed. 



Deep-sea soundings have received much attention during the last 

 thirty years. The first attempt at them appears to have been made 

 by Captain Constantine John Phipps, during his Arctic Expedition in 

 1773. He sounded a depth of six hundred and eighty-three fathoms 

 with a lead weighing one hundred and fifty pounds, which appears 

 to have sunk about ten feet into the mud. Determinations of the 

 temperature of the sea water and of its density were made at the same 

 time. Captain John Ross employed, during his Arctic voyage of 1818, 

 one of the earliest satisfactory instruments for bringing up a consider- 

 able quantity of the bottom mud in deep water, with which he was 

 able to ascertain the temperature at any depth. 



A contemporary of Ross, the younger Scoresby, observed that, 

 when in sounding at great depths the ordinary deep-sea line and lead 

 are used, the increasing weight of line, in proportion as more of it is 

 required, renders less certain the determination of the moment when 

 bottom is reached. He has also left the record of the first observa- 

 tion of the effects of the enormous pressure which is acting under the 

 deep waters. The Americans have introduced the method of using 

 fine twine and a heavy weight, both of which may be sacrificed at 

 every sounding, to obviate the inconveniences arising from overweight 

 of rope. The practice of observing the rate at which successive equal 

 lengths of line pass out has been found useful in cases where ordinary 

 observation or feeling does not sufiice to indicate when the shot has 

 reached the bottom. Iron wire was first used instead of twine about 

 1850, by Lieutenant Walsh, of the United States schooner Taney. 



When the surveys for telegraphic cables were begun, it became 

 important to ascertain the nature of the ground at the bottom. The 

 apparatus invented by Midshipman Burke, of the United States Navy, 

 in 1854, answered this purpose. It consisted of a cannon-ball with a 

 hole drilled through it. Through this hole passed a straight rod. 



