Caroline. Look, Emily, as Mrs. B. fills it, how the water rises in the goblet, to maintain an equilibrium with that in the tube.
Now, Mrs. B., will you let me fill the tube, by pouring water into the goblet?
Mrs. B. That is impossible. However, you may try the experiment, and I doubt not that you will be able to account for its failure.
Caroline. It is very singular, that if so small a column of water as is contained in the tube, can force up and support the whole contents of the goblet; that the weight of all the water in the goblet, should not be able to force up the small quantity required to fill the tube:—oh, I see now the reason, the water in the goblet, cannot force that in the tube above its level, and as the end of the tube, is considerably higher than the goblet, it can never be filled by pouring water into the goblet.
Mrs. B. And if you continue to pour water into the goblet when it is full, the water will run over, instead of rising above its level in the tube.
I shall now explain to you the meaning of the specific gravity of bodies.
Caroline. What! is there another species of gravity, with which we are not yet acquainted?
Mrs. B. No: the specific gravity of a body, means simply its weight, compared with that of another body, of the same size. When we say, that substances, such as lead, and stones, are heavy, and that others, such as paper and feathers, are light, we speak comparatively; that is to say, that the first are heavy, and the latter light, in comparison with the generality of substances in nature. Would you call wood, and chalk, light or heavy bodies?
Caroline. Some kinds of wood are heavy, certainly, as oak and mahogany; others are light, as cedar and poplar.
Emily. I think I should call wood in general, a heavy body; for cedar and poplar, are light, only in comparison to wood of a heavier description. I am at a loss to determine whether chalk should be ranked as a heavy, or a light body; I should be inclined to say the former, if it was not that it is lighter than most other minerals. I perceive that we have but vague notions of light and heavy. I wish there was some standard of comparison, to which we could refer the weight of all other bodies.