THE SHIP AND ITS EQUIPMENT 



29 



/4 



any moment than what is necessary to counteract the weight of 

 the length of line paid out. Thomson obtained this by means 

 of a brake, a hemp line running in a separate groove at the side 

 of the big wheel, and passing from there to a block, through 

 which the brake could be tightened by means of weights. 



Sir William Thomson used a plummet weigh- 

 ing 34 lbs., and commenced his sounding with 

 a counter-weight of 10 lbs, on it. This was 

 sufficient to run out the line at the rapid rate of 

 2000-3000 fathoms in thirty to fifty minutes. 

 Gradually, as more line was paid out, the 

 counter-weight was increased proportionately to 

 the length of wire in the water (12 lbs. for each 

 1000 fathoms of wire), and this caused the wheel 

 to stop almost instantaneously when the bottom 

 was reached. The depth could be ascertained 

 from the number of revolutions on the register. 

 1^ If the wheel did not stop instantaneously, an 



SL ^ error would result in the determination of the 

 ^K^^K depth, and if the steel line came into contact 

 SBHb with the bottom, it easily kinked, and the 

 ^^HpF plummet was likely to be lost. To obviate this 

 ^^■^ a few fathoms of hemp rope were inserted be- 



^H tween the plummet and the steel line. 



^B Obviously this sounding machine is a great 



■ advance on the old hemp lines. ^ Economy of 



space, smaller weights, greater speed, less fric- 

 tion in the water (and consequently a more 

 perpendicular line, resulting in greater accuracy), 

 are some of the advantages. For this reason 

 attempts have continually been made to improve 

 Thomson's machine, and in the course of time 

 a number of very good sounding machines have 

 been constructed, amongst others those of Le 

 Blanc, Sigsbee, and Lucas. Sigsbee's sounding- 

 tube is shown in Fig. 6. All of them are based 

 on Thomson's model ; thus Sigsbee says of his own admirable 

 machine : " The modification or improvement made by me on 

 the original Thomson sounding- machine lies chiefly in the 

 employment of a peculiar kind of accumulator, and its adap- 



^ It is interesting here to observe that the " Challenger" hemp line could be used for sound- 

 ing in depths down to 26,000 fathoms before reaching its breaking strain, whereas the wire could 

 only be used down to a depth of 16,700 fathoms. Depths beyond 26,000 fathoms, should such 

 depths exist, could not be explored by either method. 



Fig. 6.— Sigsbee's 

 Sounding -Tube. 

 (From Brennecke.) 



Recent 



sounding 



machines. 



