18 



SUBMARINE CABLE LAYING AND REPAIEING. 



bottoms except soft ooze, in which it sinks without impact. 

 Whenever the jaws come up unclosed after touching bottom, it 

 is a sure sign that the bottom is soft mud. In this particular 

 design the sinker is heaved up with the sounding wire. 



On the occasion of the " Challenger " Expedition Mr. J. Y. 

 Buchanan devised instruments (for use in conjunction with 

 the sounding line) which indicated the depth by the barometric 

 method and gave very concordant results. These instruments 



Fig. 13. — Lucas's Snapper, for bringing up Specimens of Sea Bottom. 



were described by him in a lecture before the Chemical 

 Society in 1878, entitled "Laboratory Experiences on board the 

 ' Challenger'" {Journal of the Chemical Society, October, 1878), 

 and are known as the water and mercury piezometers (Fig. 14). 

 This method was adopted for the reason that the sounding line 

 is sometimes affected by deep-water currents, which cause 

 errors in the measurement of depth. Generally the effect of 

 these currents is noticed by the streaming out of the line, 

 and the ship has to be manoeuvred to follow it and endeavour 



