1833.] Means of making Ice by the Natives of Bengal. 89 
heated by contact with the earth becoming specifically lighter and ris- 
ing on the atmosphere. By the continual operation of these causes an 
accumulation of caloric in the earth is prevented during the day, and 
as soon as the sun sets, the increase of heat is checked and the night 
is generally cool under a clear and sparkling firmament even during 
the hottest season. This is in consequence of the generality of bodies 
on the face of the earth radiating caloric in large quantities, especially 
when exposed to the clear sky, as they receive few rays from the neigh- 
bouring bodies in return for what they radiate into space. So power- 
ful are these causes in producing a great degree of cold, that in very 
favourable mornings drops of dew may sometimes be found congealed 
in Bengal upon thatched roofs, and upon the leaves of some plants 
during the cold weather. The cooling process advances more rapidly 
than could be supposed by one who has not experienced it himself, and 
proved the justness of his feelings by the aid of the thermometer. In 
the open plain in which the ice is made, I have seen the temperature of 
the air four feet above the ground fall in the time the sun took to de- 
scend the two last degrees before its setting from 70. 5° to 57°. 
Pieces of glass and tin were placed under the common dishes in the 
ice-beds : in the morning they were carefully examined, and their under 
surfaces were covered with large drops of moisture. A piece of glass 
eight inches long and seven broad was placed on the evening of the 
24th January, 1832, under an ice plate among the other dishes upon 
the straw in the beds, after it had been weighed; next morning, 
the dish was found to have gained 120 grains in weight, and, as 
there was no ice, the water was found to stand at 34°. A dish placed 
upon a plate of tin similarly situated with the last, gained 60 grains, 
and the water stood at 38°. On the 26th January, there was very 
little ice upon the plates, and a piece of glass and another of tin of the 
same size as the last were placed under two dishes which had been ac- 
curately weighed. In the morning the dish upon the tin had very 
little ice upon its surface, and had gained 70 grains ; the dish upon the 
glass had no ice and had gained 160 grains. 
(17th January, 1832.) This evening the following varieties of dishes 
were placed among the common dishes. A brass dish of the same 
shape and size as the common unglazed dishes weighed the same even- 
‘ing and morning. On another morning the experiment was repeated 
with the same result. The ice however was thicker and more equal 
throughout on the brass dishes than on any of the others; as water 
boils more readily in metal, so it freezes more readily—hence little 
N 
