414 E/efts of Gravity on Fluids [Book VII, 



maybe obferved generally to take place, foon after 

 mixing two heterogeneous fluids together, unlefs this 

 effect is counteracted by feme more powerful caufe* 

 It has been obferved, that the particles, according to 

 their weight, prefs independently of each other. Thofe 

 therefore which have the moil denfity, having more 

 power to gain pofteffion of the lower part of the 

 vefiel which contains them, oblige the others to yield 

 and refign their fituation - y and hence a feparation is 

 effected. When oil and water, for inftance, have 

 been well lhaken together, and afterwards the whole 

 left in a (late of reft, the water, having more denfity 

 than the oil, takes the lower pdfition and the oil rifes 

 to the furface. If this effect does not take place, it 

 is owing to the intervention of one of the following 

 caufes. Firil, a kind of elective attraction, which 

 may exift between the particles of different fluids, as 

 \vhen water and wine are mixed together, the water, 

 though heavier than the wine, does not feparate itfelf. 

 Secondly, the vifcofity of one of the fubflances, as 

 when the whites of eggs are beaten together, and by 

 that means a confiderable quantity of air mixes with 

 them j the air, though much lighter, has not power to 

 difengage itfelf from the matter in which it is en- 

 veloped, in order to effect its efcape. 



If two fluids of different denfities are placed in a 

 ftate of equipoife with each other, and have the fame 

 bafe, their perpendicular heights above the horizon 

 will be in a reciprocal ratio to their denfities or fpecific 

 gravities. 



If, for exampie, mercury is put into an inverted 

 fiphon, and water is poured into one of the branches, 

 in order to elevate the mercury in the other branch 

 one inch above its lever, it is neceffary that the water 

 Ibould be about thirteen inches and an half high. The 



height 



