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XXXIT. Observations on the relative Temperature of the 

 Sea and Air, and on other Phcenomena, made during a Voyage 

 from England to India. By the Rev. J. H. Pratt, M.A., 

 Member of the Asiatic Society of Bengal. 



To the Editors of the Philosophical Magaziiie and JoiirnaL 

 Gentlemen, 



T SEND you the accompanying observations on the relative 



temperature of the sea and the superincumbent air made 

 at various latitudes and longitudes on a voyage from England 

 to India, in case you should deem them of sufficient import- 

 ance to give them a place in your valuable Magazine. 



I regret tliat they do not extend through the whole voyage. 

 It was not till after passing the Cape that I recorded any 

 observations. I was anxious to see what effect the Mozam- 

 bique Channel had upon the currents ; and after that I con- 

 tinued my observations up to the Bay of Bengal. 



I have also given the result of a few observations on the 

 velocity of the waves of a swell in unfathomable water. 



Once or twice I attempted to ascertain the temperature 

 of the sea water at a considerable depth, such as 40 and 

 100 fathoms. The method I adopted was this : I sunk a 

 quart bottle, full of sea-water and well-corked, by means of 

 a line, and allowed it to remain a considerable time (as an 

 liour or more), that the water within the bottle might attain 

 the temperature of the surrounding water by conduction. I 

 then drew it up with great rapidity (perhaps in 1^ minute), 

 instantly uncorked the bottle, and tried the temperature. 

 When I poured the water into a glass it would change its 

 temperature very litde in 5 or 10 minutes ; so I felt assured 

 that no great change could have taken place in its passage 

 from its lowest depth. I should have made more of these 

 observations, but the utter impracticability of sinking a bottle 

 well, except in a dead calm, prevented this. One day I had 

 a bottle 200 fathoms deep for one or two hours; a gentle 

 breeze sprang up, my bottle towed astern, and in pulling it 

 in the line broke ! 



A notice of my observations will be seen in the accompany- 

 ing tables of temperature. 



I am. Gentlemen, yours, &c. 



Bishop's Palace, Calcutta, JoHN HenRY PraTT. 



March '22, 1839. 



