.SVA' W/UJAM SIEMENS, l-'.K.S. 381 



.iini: the position of the- vessel when tin- cable was buoyed 

 would never have arisen, and much anxiety and time would have 

 1 in recovering the end. In cable-laying a bathometer 

 is more particularly of use, because the amount to which tho 

 retardiug-brake has to bs weighted bears a definite relation to the 

 depth of sea traversed ; and an accurate knowledge of that depth 

 is essential to prevent either loss of cable from excessive slackness, 

 or permanent danger through an insufficiency. 



A bathometer of careful construction would be extremely useful 

 in increasing our knowledge of the depth of the ocean, whilst 

 instruments of inferior accuracy would serve the useful purpose of 

 furnishing the navigator with timely warning of approaching 

 shallows. 



It is chiefly with a view to this latter result that I venture to 

 place my inquiries into this subject before the Royal Society. In 

 doing so I wish to acknowledge the valuable assistance I have 

 received from Mr. Bamber and Dr. Higgs, the former having con- 

 ducted the experiments to determine the influence of temperature 

 <>ii the elasticity of springs, and effected the adjustment of the 

 i ustriiments on land, while the observations on board ship were 

 taken by Dr. Higgs. 



ADDENDUM. 

 ON AX ATTRACTION-METER. 



At the reading of the foregoing paper, I exhibited an instrument 

 for measuring horizontal attractions, which, at the same time, 

 illustrates the action of the bathometer. This instrument 

 (Plate 33) consists of a horizontal tube of wrought iron loo 

 millims. long, terminating at each end in a horizontal transverse 

 tube of cast iron of GO millims. diameter and 300 millims long. 

 The first-named horizontal tube is partially closed at its ends, and 

 communicates with the transverse tubes below their horizontal 

 mid section. The transverse tubes communicate also by means of 

 a horizontal glass tube of 2 millims. diameter at a superior level to 

 the former. 



The whole apparatus being mounted upon three set-screws is 

 filled to the level of the half-diameter of the transverse tubes with 

 mercury, which mercury fills also the whole of the longitudinal 



