Page:Popular Science Monthly Volume 76.djvu/203

Rh The collection of biological gear and tackle is much less complete and less advantageously displayed. There are samples of dredges, tangles, trawls, tow-nets, plankton nets, plankton nets of the Hensen, closing-net of Nansen and young-fish net of the Helgoland pattern.

The oceanographical exhibit in rooms 8 and 9 is original in design and execution and contains unique and instructive displays designed to facilitate by comparative methods the quick and easy comprehension of the fundamental facts of oceanography. Marble blocks are used to represent the relative volumes of the globe, the sea, the land above sea-level, and in the continental blocks (above 2,300 m. below sea-level). In a similar way their relative weights and those of the atmosphere and of the dissolved salt in the sea are shown, as are also the quantity of salt and the proportions of the various substances dissolved in sea water. A very striking illustration of the quantity of salt in the sea is shown by a comparison, to scale, of the thickness of the crust left on the sea bottom on evaporation of the sea, with a model of the royal castle at Berlin to the same scale. The relative elevation of the continents and depths of the seas are shown by plastic reliefs. Models of a transatlantic liner on columns of blue glass bring in vivid contrast the conditions as to depth in the North Sea, the Atlantic and the greatest known ocean depths. Movable mechanisms illustrate wave motion, while the effect of breakers on steep and flat coast line is shown by photographs and examples of erosion.

The biological exhibits are striking in their design and educative in purpose. There is little attempt at a systematic exhibit of marine