Mr Meikle on finding the Dew-point, i!Jt. 319 



beautiful printing machinery used in the Bank of Ireland, and 

 in this city the plan has been found useful in making up 

 gas-fittings, and even in such heavy work as screwing the 

 shoulders and the nuts of the axles of carriages. 



On finding the Dew-point, S^c, from the Cold induced by the 

 Evaporation of Water. By H. Meikle, Esq. Commu- 

 nicated by the Author. 



I MIGHT have felt a little flattered by the approbation which 

 the ingenious author of the article Vol. xvii. page 330, of this 

 Journal, has bestowed on my scheme for finding the dew-point, 

 had he not coupled it with a weighty charge of error. To ren- 

 der this " apparent," he brings forward an " example"" in which 

 air at the high temperature of 114° is to be " absolutely dry," 

 and the dew-point " infinitely low ;" though the slightest reflec- 

 tion might have satisfied him that neither this far-fetched ex- 

 ample, nor any thing at all approaching to it, can ever occur. 

 I have always maintained, and that gentleman admits, that con- 

 fined air can never be absolutely dry if the vessel at same time 

 contain the bulb of a thermometer having a wet covering. Un- 

 confined air again is never found absolutely dry, and more espe- 

 cially at a temperature so very high as 114° ; for, in such a case, 

 I should think it rare for the dew-point to go even so low as 

 60°, in place of descending infinitely low. Indeed, I do not 

 recollect of a case of any sort being recorded, in which the ex- 

 ternal air in a state of free circulation did not contain more 

 than a fourth of the whole moisture required for complete satu- 

 ration at the actual temperature. It is therefore no disparage- 

 ment to the graphic scheme that it does not embrace an extreme 

 and imaginary case with air absolutely dry. Should it fortu- 

 nately turn out to have no other fault, it will fully answer my 

 expectation ; for, in proposing that method, I distinctly went 

 on the supposition that it might require some amendment, and 

 I therefore accompanied it with suggestions for remedies, should 

 such be found necessary. These, our author might Iiave seen, 

 were capable of modifying the results very considerably. 



My design in bringing forward the hyperbola was not to give 

 a geometrical construction for finding the dew-point, but pro- 



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