. The Americana : a universal reference library, comprising the arts and sciences, literature, history, biography, geography, commerce, etc. of the world. ables. Henry the Navigator was the first whoconstructed a tolerably reliable sea-chart, andlaid the foundation of hydrography as a was in the 15th century. In France andother countries, institutions specially formed forteaching navigation are called hydrographicalschools. The hydrographic office is now an im-portant department of the naval administration,its officers consolidating into available maps theresults of the observatio
. The Americana : a universal reference library, comprising the arts and sciences, literature, history, biography, geography, commerce, etc. of the world. ables. Henry the Navigator was the first whoconstructed a tolerably reliable sea-chart, andlaid the foundation of hydrography as a was in the 15th century. In France andother countries, institutions specially formed forteaching navigation are called hydrographicalschools. The hydrographic office is now an im-portant department of the naval administration,its officers consolidating into available maps theresults of the observations sent to them fromtime to time by those engaged in exploring expe-ditions, and by navigators fror all parts of theworld. See Surveying. Hydrolite. See Gmelinite. Hydrometer, an instrument for determin-ing the specific gravity of fluids. When a solidbody floats in a liquid, and displaces a quantityof the liquid, it is supported by the same upward HYDROPATHY — HYDROPHOBIA pressure that formerly supported the liquidwhich it displaces. The Weight of the. solidbody is thus equal to the weight of the liquidthat it displaces. Hence, the depth to which. Fig. i.— Forms of Hydrometer. the same solid body is immersed in a liquid isgreater as the density of the liquid is less, andless as the density of the liquid is greater. And,likewise, the weights required to immerse agiven body equally deep in various liquids areinversely proportional tothe densities of the each of these princi-ples a form of hydrom-eter is founded. One iscalled the constant weighthydrometer, the other theconstant volume hydrom-eter. The first, usuallymade of glass, is shownin Fig. I. It has a largehollow bulb, and belowthat a smaller bulb,weighted with mercury,to make the instrumentfloat upright and it issurmounted by a cylindri-cal glass stem which isgraduated, the divisionsbeing usually marked ona piece of paper enclosedwithin the stem. The jjadepth to which the hy- fljdrometer sinks in theliquid gi
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