Formation of Ice in India, 217 



most any other. The old story of evaporation being at the bottom 

 of the process, and porous pans being necessary for its success, 

 is repeated by one author after another, although nothing 

 can be more erroneous. In respect to the first, it seems suffi- 

 cient to observe, that, when ice is produced in temperatures 

 above the freezing point, a plentiful deposition of dew is al- 

 ways going on, which seems to be altogether inconsistent with 

 the idea of the air being in a state capable of receiving fresh 

 accessions of moisture. I have also found, by repeated experi- 

 ments, that ice may be produced, although a thin film of oil 

 be spread over the surface of the water ; the latter being con- 

 tained in glazed plates, which indeed answer much better than 

 the porous pans of the country, the ice in them being inva- 

 riably thicker, and the water, when it does not actually freeze, 

 somewhat colder than the similarcontents of porous pans placed 

 in exactly the same situation. The fact is, that the natives 

 use porous pans from necessity, there being no other descrip- 

 tion of crockery ware manufactured in the country ; but so 

 well are they aware that the porosity of the vessels is of no ad- 

 vantage, that they usually rub them with grease for the 

 purpose, I was informed long ago, of more easily extracting 

 the ice; — but also, I now fancy, because it must tend to 

 facilitate the process, by keeping the straw, upon which they 

 are placed, in a perfectly dry and non-conducting state. 

 The only author that I have read, who has treated this 

 subject properly, is Dr Wells in his Treatise on Dew. I 

 have repeated many of his experiments, and sometimes with 

 singular results. On one occasion, a turban being suspended 

 across the ice pit, three feet above the pans, it, as it always 

 does, prevented the formation of ice in those immediately un- 

 der it ; and in several which it only partially covered, ice was 

 formed on the half of the water out of the perpendicular line, 

 while that immediately under the turban was fluid. Two 

 strings crossing each other, and placed at a less height above 

 a pan, will also divide the ice into four quarters ; but it is ob- 

 vious that these results will not always be obtained ; for if the 

 temperature be rather lower than would be necessary to freeze 

 the water, supposing no impediment to exist, the whole may 

 be frozen although partially covered ; and, on the other band. 



