Fig. 11.—A A, water in tube seeks a level.
"You have not shown me anything new," I said; "my text-books taught me this."
"True, I have but exhibited that which is the foundation of your philosophy regarding the surface of liquids. Let me proceed:
"If we pour a solution of common salt into such a U tube, as I do now, you perceive that it also rises to the same level in both ends."
"Of course it does."
"Do not interrupt me. Into one arm of the tube containing the brine I now carefully pour pure water. You observe that the surfaces do not seek the same level." (Figure 12.)
Fig. 12.—A, surface of water. B, surface of brine.
"Certainly not," I said; "the weight of the liquid in each arm is the same, however; the columns balance each other."
"Exactly; and on this assumption you base your assertion that connected liquids of the same gravity must always seek a common level, but you see from this test that if two liquids of different gravities be connected from beneath, the surface of the lighter one will assume a higher level than the surface of the heavier."