282 



OF THE EQUILIBRIUM OF FLOATATION. 



into the lower of which is introduced a small quantity of mercury or 

 leaden shot, for the purpose of preventing the instrument from over- 

 turning, and causing it to float steadily in a vertical position, or per- 

 pendicularly to the surface of the fluid in which it is immersed. 



Numerous schemes have been promulgated by different ingenious 

 and experienced philosophers for the improvement of this instrument ; 

 but however much the forms which have been recommended may differ 

 among themselves, yet the general principle is the same in all. 



The following is a list of the principal writers who have registered 

 their improvements in the annals of science, viz. 



Desaguliers, Guyton, Nicholson, Speer, 



Adie, Charles, 



Atkins, Clark, Dicas, 



Brewster, Deparcieux, Fahrenheit, 



Jone 



Quin, 

 Sikes, 



and 

 Wilson. 



355. It would be quite superfluous to detail the various alterations 

 and improvements suggested by these authors; suffice it to say, that in 

 all there is something different and in all there is something common ; 

 but that which merits the greatest share of our attention, by reason 

 of the extreme delicacy of its indications -and the simplicity of its 

 construction, is the hydrometer of Deparcieux, which was presented 

 to the Academy of Sciences in the year 1766. 



This instrument, which was intended by its inventor to measure the 

 specific gravities of different kinds of water, is 

 represented in the annexed figure, where AC is a 

 glass phial about seven or eight inches in length, 

 loaded with mercury or leaden shot, to prevent it 

 from overturning; and in order that no air may 

 lodge below it, when it is immersed in the fluid, the 

 lower part is rounded off into the form of a spheric 

 segment. 



In the cork of the phial at A, is fixed a brass wire 

 of one twelfth of an inch in diameter, and from thirty to thirty six 

 inches long, or of any other length which may be found convenient 

 for the purpose, but such, that when the phial is loaded and immersed 

 in spring water of a medium temperature, the entire phial and about 

 one inch of the wire should be below the graduated scale DH, which 

 is fixed upon the side of the tin vessel DEFG ; to the other end, or 

 summit of the wire, is attached a small box B, intended for containing 

 the minute weights which it may be found necessary to apply, in order 

 to cause the instrument to sink to a certain fixed point in the 



