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Observations on the Temperature and Moisture of the Atmo- 

 sphere, and on the Temperature and Specific Gravity of the 

 Surface Water of the Northern Atlantic. By ROBERT Law- 

 SON, Assistant-Surgeon, 47th Regiment. Communicated 

 by the Author. 



The distribution of temperature in the sea and superincum- 

 bent atmosphere is very imperfectly known. Were a few 

 only of those who annually cross the Atlantic, to bestow some 

 little trouble on the subject, a mass of information would be 

 rapidly accumulated regarding it, which would be of the great- 

 est value. During a voyage from Gibraltar to Barbadoes in 

 1841, and from that island to England in 1842, I made a 

 series of observations on these points. The results, which pos- 

 sess some features of interest, are given below. 



The temperatures were observed by instruments, the errors 

 of which were carefully ascertained (they are known every- 

 where to be about 0°-l Fahr.), and have been allowed for in 

 the tables. The dew-point is calculated, from the indications 

 of a wet-bulb thermometer, by Dr Apjohn's tables, and, from 

 some comparative experiments I made in the West Indies, may, 

 I think, be depended upon to within a fraction of a degree. 



The specific gravity of the water, taken during the voyage 

 home, was determined soon after my arrival. The balance 

 employed indicated distinctly ^V of a grain, when loaded with 

 4000 grains. The water was weighed in a bottle which held 

 about 1000 grains of distilled water, and every care was taken 

 to ensure accuracy, by ascertaining the errors of the weights 

 employed, and weighing the bottle in both pans of the balance. 

 The specimens were weighed at temperatures within a few 

 degrees of 62° Fahr., and the weights subsequently reduced to 

 62°, by data derived from observing the rate of expansion of sea- 

 water above and below that point, the effect due to the expansion 

 of the glass having been eliminated in all. The most trouble- 

 some point was to determine the temperatui-e of the specific 

 gravity bottle and its contents ; and, as a difference of 0°-l Fahr. 

 throughout the mass corresponds with a unit in the fifth place 

 of decimals in the specific gravity, it is clear that a slight error 

 in the temperature would affect it sensibly : by placing the 

 bottle, however, full of salt water, into a small vessel of water, 

 Bnd gently agitating both with thermometers, the moment 

 their respective temperatures coincided was shewn, when the 



