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THE VOYAGE OF H.M.S. CHALLENGER. 



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It will be evident from this description that the whole secret of the successful disen- 

 gaging of the weights at the bottom rests on the spring of the rod being nicely adjusted 

 as to strength — that is, it must not be so strong as to push the wire off the stud directly 

 a portion of the weight of the sinkers is removed by letting go the line, and it must be 

 strong enough to spring sharply back into its place directly the whole weight is removed. 

 The system adopted was to ease the sinkers down without jerks for about 400 or 500 



fathoms, so that when the line was eventually let go the 

 friction of the 500 fathoms of cordage passing through 

 the water above the rod was sufficient to keep the requisite 

 strain on the spring. By letting go the line suddenly 

 when the sinkers were near the surface, they were found 

 frequently to disengage at once. 



The Baillie rod (which is an invention of Navigating 

 Lieutenant Baillie, R.N.) is a much better apparatus 

 than the Hydra rod, as the arrangement for disengaging 

 the sinkers is entirely independent of springs. It 

 consists of an iron cylinder with a butterfly valve at 

 the bottom f and a brass tube b on the top, which 

 screws on to the cylinder (see fig. 14). The brass 

 tube is bevelled at its upper end, and in it is a cylin- 

 drical iron w T eight c which slides backwards and for- 

 wards, the length of movement being regulated by a 

 slit d cut in the side of the brass tube b, through 

 which a stud, fastened on to the weight, projects. 

 Attached to the upper part of the weight is a flat bar of 

 iron, which protrudes through another slit, cut in the 

 pointed top of the brass tube, and this bar moves in or 

 out as the weight is moved backwards or forwards. The 

 upper part of the flat bar is narrow r ed abruptly so as to 

 form two shoulders, and the distance of these shoulders 

 from the weight is so regulated that when ,the stud 

 fastened to it is at the upper end of the slit these 

 shoulders are above the brass tubing, but when the weight falls dow T n, and the stud 

 rests on the lower end of the slit, they are concealed by the tubing, which thus 

 forms a sort of sheath for the shoulders. The upper part of the bar is furnished with a 

 ring to facilitate the attachment of the lead line. When the sounding rod is lifted by this 

 ring the weight inside the brass tubing is pulled up until the stud fastened to it is at the 

 upper end of the slit at the side of the tubing, and consequently the shoulders on the 

 iron bar are above the head of their conical sheath, and so long as the rod is suspended 



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Flo. 14.— Baillie Sounding Machine. 



