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the wire is about the same, the great gain being, in reeling in. For instance, Prof. Wyville Thomson states in his “Depths of the Sea,” that sounding from H. M. S. “Porcupine,” in 2435 fathoms, the deepest cast made from that vessel, the time occupied in descent of the line was 33 minutes, 35 seconds, and in “heaving up” 2 hours, 2 minutes; while on board the Tuscarora a cast was had in 2565 fathoms, the time of running out being 31 minutes, 7 seconds, and of reeling in, 39 minutes, 42 seconds, or a gain of nearly a hundred per cent in the total time occupied in the cast. And I can but consider the difference in accuracy in favor of the wire, to be somewhat in the same proportion; for a sinker attached to that light, thin attenuated material, goes straight to the bottom like a plummet dropping into a well, opposing an almost inappreciable surface to the action of ocean currents, while rope or cord, comparatively heavy, presents a not inconsiderable and rough surface, developing a good deal of friction as it runs down to great depths, and curves and bends in all directions in meeting the under currents, and the percentage of stretch should by no means be lost sight of.
When sounding, serial temperatures are taken at the same time from the topgallant forecastle with a duplicate Thomson machine. For instance, if the temperature is desired for every 100 fathoms below the surface down to 500 fathoms, a 7 lb. lead and a Miller-Casella thermometer is attached to the wire. Then the wire is allowed to rim out slowly till the 100 fathom mark is reached and another thermometer is attached, and so on, till the desired depth is reached, and thus, at one serial sounding, the several temperatures are taken. The thermometers are very accurate in their indications, as found by their close correspondence in the many series of temperatures observed.
In the Central North Pacific, from San Diego to the Bonin Islands, the under temperature curve of 40° F. is found to range from 400 fathoms to 500 fathoms in depth. At 1200 fathoms about the lowest temperature is reached;
