ON DEW, &c. 267 



must be very small ; as it does not appear that 

 the old are ever laid aside on account of their 

 unfitness. 



In a like way may be explained, without the 

 aid of cold produced by the evaporation of 

 moisture from the outsides of the pans, another 

 fact mentioned by Mr. Williams, that ice was 

 often found by him in those vessels, while water 

 contained in a china plate, surrounded by them, 

 had none ; since the thin and dense substance 

 of the plate must have transmitted more readily, 

 than the thick and rare substance of the pans, 

 the heat of the straw to the water. 



5. In accounting for the making of ice in 

 Bengal, it is requisite to show, not only how the 

 first film is produced, but also, in what way the 

 thickness of this film is afterwards increased. 

 If evaporation be the cause of this increase, it 

 follows, that a plate of ice in the night-time, 

 and in the stillest air, both unfavourable to that 

 process, must yet emit as much moisture, as is 

 necessary for the production of a cold, accord- 

 ing to Mr. Williams, of at least 14, and accord- 

 ing to Sir H. Davy of at least 18; a conclu- 

 sion, as it appears to me, of itself sufficient to 

 destroy the credit of the theory, from which it 

 is drawn. 



While attending to this subject, I became 

 desirous of acquiring some knowledge of the 



