Page:Smithsonian Report (1898).djvu/493

Rh the Gulf Stream. The accumulation of the resulting debris of rocks forms the banks of Newfoundland.

These ice fields are of particular interest because of the fear they inspire, because of the shoals formed by their melting, and particularly because the chilling occasioned by their contact with an atmosphere warmer and more saturated with moisture, gives rise to heavy fogs. Hundreds of disasters would be avoided, enormous economy in the transportation of merchandise would be effected if we could succeed in understanding and foreseeing these phenomena. The admirable pilot charts published every month by the Hydrographic Bureau at Washington seek to solve the problem empirically, noting to what latitude the ice fields descend each year, observing their number, and establishing the probabilities concerning them according to the average of numerous observations. Fogs due to analogous causes—that is to say, to marine currents—are frequent in the northern or even the temperate region, on the North Sea, the English Channel, and on the Atlantic coasts of England and France. Everywhere they are the terror of sailors; ships move in them bewildered, advancing at the risk of running ashore or colliding with another vessel, while if they remain stationary they are in danger of being themselves struck, and in any case they lose time, that precious commodity whose price rises higher every day. The ability to foresee their presence, or if overtaken by them to find the course and follow it with certainty, would be the immediate consequence of the perfecting of oceanography.

Some attempts at this have been crowned with success. The position of a ship in the ocean is usually determined by the aid of astronomical coordinates. According to the observed position of a heavenly body, star or sun, the observer calculates his own position on the surface of the waves. Knowing where he is and where he is going, nothing is easier for him than to follow his course. But the indispensable condition is to see the star; this the fog renders impossible. This impossibility is the cause of most shipwrecks. However, the position can be otherwise determined. If we have a so-called bathymetric chart, plainly indicating by means of contour lines the depth of the water at each point, and another chart drawn up after a series of soundings and of preliminary analyses showing in the same part of the sea the changing nature of the bottom, here sand and there mud of one kind or another and there rocks, by a single cast of the lead a vessel lost in the midst of the ocean can determine her position. The depth of the sounding will confine the observation to the area for which the bathymetric chart gives this depth. If, moreover, care has been taken to fit the sounding lead with some means by which a sample of the bottom may be brought up, the area covered by this kind of bottom may be looked up on the lithologie chart, and, combining this information with the preceding, one will be able to ascertain his position almost exactly. Excellent