1874.] Temperatures of the Sea at various Depths. 465 



pressure forced water into the cylinder. For these corrections were 

 made. 



In 1839, MM. Martins and Bravais made a series of observations in 

 the sea between Norway and Spitzbergen with instruments carefully 

 protected against pressure by means of glass tubes or metal cylinders. 

 They used both self-registering thermometers (fhermometrographes) 

 and "Walferdin's self -registering overflow thermometers, sending down 

 two to four of each in every sounding, and taking the mean of the readings. 

 These probably are amongst the most accurate observations on record. 

 To a great extent they confirm those of Scoresby; and they further 

 showed that the bottom-temperature near the Spitzbergen glaciers was 

 about 29 E. None of the soundings exceeded 3000 feet. 



In 1857, the late Admiral EitzEoy furnished Captain Pullen with ther- 

 mometers specially constructed to resist pressure, and some very interest- 

 ing, though somewhat variable results, were obtained therewith. On two 

 occasions a temperature of 35 E. was recorded one in the Atlantic, 

 26 46' S., at a depth of 16,200 feet, and the other in the Indian Ocean, 

 at a depth of 13,980 feet. 



"With regard to the many observations made with unprotected instru- 

 ments, they mostly admit of correction, which renders them available. 

 Such corrections have been independently computed, with little difference, 

 by Du Petit Thouars, Martins, Airne, and the late Dr. Miller. The 

 author, taking the mean of their estimates, uses as a coefficient 1 E. for 

 every 1700 feet of depth. 



In the third part of the paper the author shows the " State of the 

 Question at the date of the Lightning Expedition." Ellis, Eorster, 

 Peron, and others early remarked on the decrease of temperature at depths 

 in temperate and tropical seas, but it was not until 1823 that Lenz 

 showed that a temperature of 35 to 36 existed at greater depths in 

 those seas. Notwithstanding this, D'Urville in 1826, misled by incorrect 

 readings obtained by previous observers with unconnected instruments, and 

 in the absence of sufficiently deep observations of his own, was led to 

 believe that the temperature in open seas at and below a depth of* 3214 

 feet (600 brasses) was nearly uniform, at 39-8 E. (4-4 C.), and that be- 

 tween the latitudes of 40 and 60 there is a belt of a like nearly uniform 

 temperature. A few years later, Arago, discussing the results obtained 

 by Du Petit Thouars, insisted that they effectually disproved this hy- 

 pothesis. Nevertheless, in 1839, Sir James E/oss made the same mis- 

 take as D'Urville, and unfortunately obtained for it a wider circulation, 

 which seems, however, to have been almost altogether restricted to this 

 country. Still, Boss's numerous observations, when viewed under cor- 

 rection, are of considerable value, though the author considers that some 

 error has occasionally crept into that uniform reading, so often recorded, 

 of exactly 39-5. Both D'Urville and Eoss wrote under the opinion that 

 sea-water, like fresh water, attained its maximum density at a tempera- 



