Indian Science and Technology in the Eighteenth Century: Some Contemporary European Accounts c18.6

c18.6

To reason physically upon this process of making ice, it may be said, that had the thermometer been suspended in the air, free from every other body capable of communicating heat, in some parts of the night during the cold months of December, January, and February, the quicksilver might have descended to the freezing point, and that water, being artfully placed in a similar situation, contained in thin porous pans, and supported by a substance little capable of communicating heat from the earth, might also freeze, and continue in a state of congelation till the heat of the morning came on. I say this may be possible; but at the same time I must beg leave to observe, that, during my residence in that quarter of the globe, I never saw any natural ice. I cannot declare that the thermometer has not descended to the freezing point during the night, because I never made the necessary observations; but the water in every other situation, excepting in the pans, has not appeared to be in a freezing state. The climate may probably contribute in some measure to facilitate the congelation of water, when placed in a situation free from the heat of the earth, since those nights in which the greatest quantity of ice has been produced, were, as I before observed, perfectly serene, the atmosphere sharp and thin, with very little dew after midnight. Many gentlemen, now in England, have made the same remarks, in their frequent visits with me to the ice-pits. The spongy nature of the sugar-canes, or stems of the Indian corn, appears well calculated to give a passage under the pans to the cold air; which, acting on the exterior parts of the vessels, may carry off by evaporation a proportion of the heat. The porous substance of the vessels seems equally well qualified for the admission of the cold air internally; and their situation being full a foot beneath the plane of the ground, prevents the surface of the water from being ruffled by any small current of air, and thereby preserves the congealed particles from disunion. Boiling the water is esteemed a necessary preparative to this method of congelation; but how far this may be consonant with philosophical reasoning, I will not presume to determine.