. A directory for the North Atlantic Ocean, comprising instructions general and particular for its navigation. Pilot guides. 638 DEEP-SEA THEKMOMETEaS. indices are brought down upon the mercury by passing a magnet along the ; Negretti and Zambia's Deep-Sea Thermometer.—It having been urged that the Miller-Casella Thermometer simply registered the coldest tem- perature passed through, without regard to depth, Messrs. Negretti and Zarnbra, scientific instrument makers, devised an apparatus by means of which the temperature can be readily ascertained at any depth as required, and if nec
. A directory for the North Atlantic Ocean, comprising instructions general and particular for its navigation. Pilot guides. 638 DEEP-SEA THEKMOMETEaS. indices are brought down upon the mercury by passing a magnet along the ; Negretti and Zambia's Deep-Sea Thermometer.—It having been urged that the Miller-Casella Thermometer simply registered the coldest tem- perature passed through, without regard to depth, Messrs. Negretti and Zarnbra, scientific instrument makers, devised an apparatus by means of which the temperature can be readily ascertained at any depth as required, and if necessary a series of temperatures could be obtained by fixing these Ther- mometers on the sounding-line at such intervals apart as may be determined. Figure 1 represents the Thermometer in the position it occupies during descent, and Fig. 2 as it appears after register- ing. The fan revolves only as the line is drawn up, and attached to it is a screw which permits the Thermometer to turn over in its frame, after the fan has per- formed a certain number of revo- lutions and the column of mer- cury previously above the bulb indicates the precise Temperature at the time of turning over. The cylindrical bulb (Fig. 3), containing mercury, has its neck closely contracted at A. When the bulb is downward, it contains sufficient mercury to fill the tube and part of the small reservoir C at the other end of the tube. When the bulb is held upward, the mercury breaks off at A, and fills C and a part of the tube, the. Fig. 2. mercury indicating the temperature on the scale, as shown in Fig. 3. A simpler form of instrument is constructed for ordinary ship's use. Sir William Siemens' Electric Thermometer is a very delicate instrument, by which the Temperature is recorded on deck at any depth desired. We cannot attempt to describe this, it being only suitable for scientific purposes. The following illustration has appeared in many previous editions of this work, and, although th
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