Hydrostatics. 47 



marked or graduated. The instrument is made 

 so that the ball sinks in water, but not entirely, 

 and therefore a part of the stem is always above 

 the surface. If it is immersed in a fluid lighter 

 than water it will sink, and less of the stem will 

 be above the surface ; if in a heavier fluid, it will 

 rise higher, and more of the stem will be visible. 

 This instrument is fully described, and its theory 

 explained more at large in the first vol. of Gre 

 gorv's Mechanics. 



