23G ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



calculation was made in designing the instrument, but 

 Mr. Siemens has preferred to compare the readings of 

 the instrument with actual soundings, in order to obtain a 

 scale. 



The instrument, which is called a bathometer, consists of 

 the following parts : A weight, being a column of mercury 

 affected by variation of gravitation ; a counterbalance, being 

 springs unaft'ected by variation of gravitation ; and an ar- 

 rangement by which variations in gravitation can be read as 

 depths in units. The column of mercury is maintained in a 

 vertical steel tube having cup-like extensions, the lower por- 

 tion being closed by a corrugated diaphragm of thin steel 

 plate, and the upper portion containing an aperture for filling 

 the instrument, having a screw stopper. The internal diam- 

 eter of the tube is reduced at the upper portion, in order that 

 the vertical oscillations of the mercury produced by the mo- 

 tion of a vessel in a sea-way may be reduced to a minimum ; 

 and the instrument is suspended in a universal joint above its 

 centre of gravity, so that it may always hang in a vertical 

 position at sea, and is inclosed in an air-tight casing, so that 

 it may not be under the influence of atmospheric changes. 

 The weight of the column of mercury is balanced at the cen- 

 tre of the diaphragm by the elasticity of the steel springs, 

 and the modus operandi of the instrument is evident ; as the 

 mercury diminishes in potential through the effects of di- 

 minished attraction, the action on the springs diminishes, 

 and these shorten upon themselves. 



There are some peculiarities in the mechanical arrange- 

 ment of the instrument which repay examination. Both ends 

 being open to the air, its indications are not affected by va- 

 riations of atmospheric pressure. With regard to tempera- 

 ture, the instrument is paratherinal. 



Professor Holden states that by the courtesy of Dr. Siemens 

 he was enabled to see the manuscript account of soundings 

 taken with this instrument on board the Faraday in October 

 and November, 1875, and in March and April, 1876. During 

 her voyage across the Atlantic at that time frequent sound- 

 ings were made with the piano-wire sounding apparatus of 

 Sir "William Thompson, and at each one of these soundings 

 the bathometer was read bv Dr. Hicks, who had it under his 

 charofe. The results are exhibited in the following: table : 



