Deep-sea sounding and dredging; a description and discussion of the method and appliances used on board the Coast and Geodetic Survey Steamer, "Blake." . ment is set by bringing the lower ends of the indicesin contact with the mercury by means of a magnet provided for thepurpose. Then, when the instrument is submitted to a higher tempera-ture, the expansion of the mixture in the large bulb depresses the columnof mercury on that side and correspondingly elevates it on the other decrease of temperature contracts the mixture in the large bulb, and bythe elastic force of the compressed air
Deep-sea sounding and dredging; a description and discussion of the method and appliances used on board the Coast and Geodetic Survey Steamer, "Blake." . ment is set by bringing the lower ends of the indicesin contact with the mercury by means of a magnet provided for thepurpose. Then, when the instrument is submitted to a higher tempera-ture, the expansion of the mixture in the large bulb depresses the columnof mercury on that side and correspondingly elevates it on the other decrease of temperature contracts the mixture in the large bulb, and bythe elastic force of the compressed air in the smaller bulb a transference ofthe column of mercury takes place in precisely the reverse manner to thatwhich occurs on a rising temperature. Thus the mercury rises in the leftlimb for a lower and in the right limb for a higher temperature. Thegreater the change of temperature the higher the point reached in therespective limbs; hence the scale on the left is graduated from the topdownwards, and that on the right from the bottom upwards. The rising ofthe mercury in either limb carries with it the index of that limb, and on g ?3 -p . r > SPECIMENS, DENSITIES, TEMPERATURES, AND CURRENTS. 109 the retreat of the mercury the index remains at the highest point bottom of the index, being the part which has been in contact withthe mercury, gives the point at which to take the reading. It was found that instruments made as described were liable to con-siderable error, in excess, amounting sometimes to as much as ten degreesin deep casts, due to the pressure of the water; the pressure, by compress-ing the large, full bulb, forced part of the contents into the capillary tube,producing the same result as an increase of temperature.* In April, 1869, Dr. D. A. Miller, vice-president of the Royal Society,proposed surrounding the larger bulb by another bulb, the latter to providea shield for the former. All thermometers styled Miller-Casella are con-structed with
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Keywords: ., bookcentury1800, bookdecade1880, bookpublisherwashingtongovtprin
