Having arrived at the conclusion that the mountains show evident signs of upheaval, let us proceed to inquire whether any movements, either upward or downward, are taking place now on the earth, or can be proved to have done so within comparatively recent times. On this question there is ample evidence at our disposal. More than one hundred and thirty years ago, Celsius, the Swedish astronomer, was aware, from the unanimous testimony of the inhabitants of the sea-coasts, that the Gulf of Bothnia was constantly diminishing both in depth and extent. He resorted to measurements in order to prove (as he thought) that the waters of the Baltic were changing their level. This was a mistaken idea; and we now understand that the level of the sea does not change, except under the influence of the daily rise and fall of the tide, which is easily allowed for. However, that was the idea then; and it survived for some time. But if the sea-level were continually sinking, the water, which, owing to the influence of gravitation, must always remain horizontal, would equally retreat all round the Scandinavian peninsula and on all our seashores. But this is not the case. Again, it would be impossible on this theory to explain the curious fact that in some parts of the world the sea is gaining on the land, while in other places it is as surely retreating; for we cannot believe that in one part the sea-level is rising, while in another (not far off in some cases) it is sinking. No body of water could behave in this irregular fashion; and the sea could not possibly be rising and falling at the same time. Hence we may take it for granted that any change that we may notice in the relative level of land and sea _must_ be due to upward or downward movements in the land. But to return to Celsius. Old men pointed out to him various points on the coast, over which during their childhood the sea was wont to flow, and besides, showed him the water-lines which the waves had once traced out farther inland. And besides this, the names of places which implied a position on the shore, former harbours or ports now abandoned and situated inland, the remains of boats found far from the sea, and lastly, the written records and popular songs, left no doubt that the sea had retreated; and it seemed both to themselves and to the astronomer that the waters were sinking. In the year 1730 Celsius, after comparing all the evidence he had collected, announced that the Baltic had sunk three feet, four inches, every hundred years. In the course of the following year, in company with Linnæus, the naturalist, he made a mark at the base of a rock in the island of Leoffgrund, not far from Jelfe, and thirteen years afterwards was able to prove, as he thought, that the waters were still subsiding at the same rate, or a little faster. In reality, he had proved, not that the sea was sinking, but that the land was rising.