DEEP SEA SOUNDING. 725 



the greatesi leptps, distinctly feel the shock of the arrest of the 

 weight upon the bottom communicated to his hand. 



Various attempts have been made to construct instruments 

 which should accurately determine the amount of the vertical 

 descent of the lead by self-registering machinery. The most 

 successful and the one most commonly used is Massey's sound 

 ing machine. This instrument, in its most improved form, is 

 shown in the accompanying cut. It consists of a heavy oval 

 brass shield, furnished with a ring at each end of its longer 

 axis. To one of these a sounding rope is attached, and to 

 the other, the weight is fastened at about a half fathom below 

 the shield. A set of four brass wings or vanes are set obli- 

 quely to an axis, so that, like a windmill or propeller wheels, 

 it shall turn by the force of the water as it descends. This 

 axis communicates its motion to the indicator, which marks 

 the number of revolutions on the dial plate. One of these 

 dials marks every fathom, and the other every fifteen fathoms 

 of descent. This sounding machine answers very well in 

 moderately deep water, and is very valuable for correcting 

 soundings by the lead alone, where deep currents are sus- 

 pected, as it is designed to register vertical descent alone. In 

 very deep water it is not satisfactory, from some reason which 

 it is difficult to determine. The most probable explanation is 

 that it shares the uncertainty inherent in all instruments using 

 metal wheel work. Their machinery seems to get jammed in 

 some way,, under the enormous pressure of the water, at great 

 depths. * 



To ascertain the surface temperature of the water of the sea 

 is simple enough. A bucket of water is drawn up, and a ther- 

 mometer is placed in it. With an observation of this kind 

 the height of the thermometer in the air should be always noted. 

 Until very recently, however, very little or nothing was known 

 vvith any certainty about the temperature of the sea at depths 

 belov the surface. Yet this is a field of inquiry of very great 



