THE BATHOMETER. 



BY DR. SIEMENS. 



LADIES and Gentlemen, I have been asked by the Depart- 

 ment to give a description of an instrument that I have 

 placed in this interesting Loan Collection, the name of which 

 is Bathometer. The name is derived from bathos the 

 depth, its purport being to measure the depth of the sea 

 without a sounding-line. It is as long ago as 1859 that my 

 attention was first drawn to this subject. Being profes- 

 sionally connected with submarine telegraphy and the 

 establishment of submarine cables, I was struck with the 

 great inconvenience arising through the want of knowledge 

 of the depth below the ship which is engaged in the 

 operation of cable laying, and as it is always interesting 

 to know the origin of an idea, I think I may * shortly 

 point out to you the nature of the difficulty which really 

 suggested this idea. In laying a submarine cable, the cable 

 passes from the tank of the ship over a stern pulley and 

 over a dynamometer into the sea. The cable would run 

 out over this stern pulley with an indefinite velocity, unless 

 it were retained by the dynamometer, and the amount of 

 retaining force necessary to prevent the cable either from 

 running out too quickly or from being laid too tight at the 

 bottom is represented by the weight of the cable hanging 

 from the ship vertically down to the bottom. If the depth 

 is a mile and the weight of the cable in sea water is one ton 

 per mile, the retaining force which has to be applied to 

 the dynamometer must be exactly one ton. If less than 

 one ton is applied the cable will run out in undue propor- 

 tion, and if more is applied it will be stretched tight upon 



