[ 176 ] 
XXXII. Ohsermtio7is on the relative Temperature of the 
Sea and Air, and on other Phcjenomena, 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 Magazine and Journal, 
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 that 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 
hour 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 minute), 
instantly uncorked the bottle, and tried the temperature. 
When I poured the water into a glass it would change its 
temperature very little 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. 
nishoi)’s Palace, Calcutta, JoHN HenrY Pratt. 
March 22, 18.39. 
