Temperature of the Sea. 47 



The thermometer has been usefully applied to determine 

 currents at sea ; and it has been proposed to employ it to de- 

 tect the vicinity of land. May not the specific gravity of sea 

 water be turned to a similar account '? Any well marked 

 change should indicate some powerful modifying influence, 

 such, in the instance of diminution, as the approach to some 

 great river, or to a region of storm and rain ; or, on^he con- 

 trary, of increase, the approach to a shore without rivers, or to 

 a region suff^ering from drought ; indications which, to the ex- 

 ploring navigator, might not be destitute of utility. 



Besides noticing the temperature of the air at 8 A.M., I often 

 observed it at other times, about noon especially, and at sunset. 

 It was commonly highest at noon, in accordance with what I 

 had observed many years ago on a voyage to Ceylon, when I 

 found, that whilst the temperature of the air was at its maxi- 

 mum when the sun was highest, that of the surface water did 

 not attain its maximum till two or three hours later. 



The low temperature of the sea and air between England 

 and Madeira in the last week in June is worthy of remark, 

 and the latter especially, compared with the heated state of 

 the atmosphere in England during the preceding week, when, 

 in most parts of the country, as well as in London, the tem- 

 perature by day was often about 70° and 75°. The marked 

 difference is suggestive of a probable advantage to be derived 

 by invalids who may have the means at their command, in 

 sailing at this season on the Atlantic as far as the latitude of 

 Madeira, or a degree or two farther south. The agreeable 

 temperature we experienced, it may be inferred from several 

 circumstances, was not singular, but of regular occurrence, de- 

 pending on the temperature of the sea and the direction of the 

 winds, which are commonly on this portion of the ocean from 

 cool regions ; circumstances to which Madeira, no doubt, is 

 mainly indebted for the coolness of its summer's climate. 

 Another recommendation of the ocean climate is, that besides 

 its agreeable coolness, and little variation by day and night, no 

 dew ever appearing, the degree of dryness of the air is favour- 

 able for most pulmonary complaints. A thermometer, used as 

 a hygrometer, generally fell 5°, compared with a thermometer 

 with a dry bulb. 



