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Account of a New Hygrometer, by George Gumming, M.D. 



The distinguished merits of Mr. Dalton must be well known 

 to every one conversant with the progress of Chemistry and 

 Meteorology ; and, in common with others, I have ever con- 

 sidered the following experiment for determining the varying 

 force of aqueous vapour in the atmosphere, as a genuine spe- 

 cimen of cautious, or inductive philosophy. ** In order to find 

 the force of the aqueous atmosphere," (says Mr. Dalton in his 

 ** Essay upon the Force of Steam or Vapour from Water and 

 other Liquids of different Temperatures," 5th vol. page 581, 

 of the " Memoirs of the Literary and Philosophical Society of 

 Manchester,") ''I usually take a tall cylindrical glass jar, dry 

 on the outside, and fill it with cold spring water, fresh from the 

 well ; if dew be immediately formed on the outside, I pour the 

 water out, let it stand awhile to increase in heat, dry the out- 

 side of the glass well with a linen cloth, and then pour the 

 water in again ; this operation is to be continued till dew ceases 

 to be formed, and then the temperature of the water must be 

 observed ; and opposite to it will be found the force of vapour 

 in the atmosphere. This must be done in the open air, or at 

 a window ; because the air within is generally more humid than 

 that without. Spring water is generally about 50°, and will 

 mostly answer the purpose the three hottest months in the 

 year ; in other seasons an artificial cold mixture is required. 

 The accuracy of the result obtained this way I think scarcely 

 needs to be insisted upon. Glass, and all other hard, smooth 

 substances I have tried, when cooled to a degree below what 

 the surrounding aqueous vapour can support, cause it to be 

 condensed on their surfaces into water. The degree of cold 

 is usually from 1 to 10 below the mean heat of the twenty-four 

 hours; in summer I have often observed the point as high as 

 58° or 59°, corresponding to half an inch of mercury in force, 

 and once or twice have seen it at 62° ; in changeable and windy 

 weather it is liable to considerable fluctuation." But the great 

 objection to this mode of experimenting, it may be observed, 

 consists in the length of time required to verify an observation, 

 to say nothing of the trouble of employing *' an artificial cold 

 mixture" for the greatest part of the year. Hence the satis- 



