HYDROGRAPHICAL SURVEY. 



183 



A glass hydrometer, with a large bulb and very- 

 slender stem, was used for determining some of 

 these specific gra^^ties ; but others were ascertain- 

 ed by weighing the water in a thin glass vessel, 

 with a ground stopper, capable of containing 1012 

 grains of distilled water. When the specific gra- 

 vities were determined at any other temperature 

 than 60°, they were brought to that standard by 

 the application of a correction derived from expe- 

 riment *. 



• Table of Changes of Specific Gravity of sea-water, for every 

 five degrees of temperature, between 30^ and 100°, applicable 

 as a correction to bring observed specific gravities to that of 

 temperature 60o. 



Sect. 



