He selected a curved glass tube, and poured water into it. The water assumed the position shown in Figure 11.
"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.)
"Certainly not," I said; "the weight of the liquid in each arm is the same, however; the columns balance each other."
B, surface of brine.
"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."
"Agreed; however tortuous the channel that connects them, such must be the case."
"Is it not supposable," said he, "that there might be two pockets in the earth, one containing salt water, the other fresh water, which, if joined together, might be represented by such a figure as this, wherein the water surface would be raised above that of the brine?" And he drew upon the paper the accompanying diagram. (Figure 13.)
