exercise at least some degree of influence in disturbing equilibrium, are not these creatures entitled to be regarded as agents which have their offices to perform in the system of oceanic circulation, and do they not belong to its physical geography? Their influences upon the economy of the sea are like those outstanding quantities which the astronomer finds in the periods of heavenly bodies. He calls them perturbations; for short, or even during considerable intervals, their effects may be inappreciable; for they are pendulums that require ages for a single vibration; but unless there was a balance provided somewhere, they would, during the progress of time, accumulate their small perturbations so as to produce disorder, and finally cause the destruction of worlds. So, too, with the salts of the sea, and those little microscopic inhabitants of its waters. They take care of its outstanding quantities of solid matter, and by their influence preserve harmony in the ocean. It is immaterial how great or how small that influence may be supposed to be; for, be it great or small, it is cumulative; and we therefore may rest assured it is not a chance influence, but it is an influence exercised by design, and according to the commandment of Him whose "voice the winds and the sea obey." Thus God speaks through sea-shells to the ocean.
488. Their physical relations.—It may therefore be supposed that the arrangements in the economy of nature are such as to require that the various kinds of marine animals, whose secretions are calculated to alter the specific gravity- of sea water, to destroy its equilibrium, to beget currents in the ocean, and to control its circulation, should be distributed according to order. Upon this supposition—the like of which Nature warrants throughout her whole domain—we may conceive how the marine animals of which we have been speaking may impress other features upon the physical relations of the sea by assisting also to regulate climates, and to adjust the temperature of certain latitudes. For instance, let us suppose the waters in a certain part of the torrid zone to be 90°, but, by reason of the fresh water which has been taken from them in a state of vapour, and consequently by reason of the proportionate increase of salts, these waters are heavier than waters that may be cooler, but not so salt (§ 105). This being the case, the tendency would be for this warm, but salt and heavy water to flow off as an under current towards the polar or some other regions of lighter water; but these creatures take
