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THE POPULAR SCIENCE MONTHLY 



that it is at a temperature of 40 Fahr., and this ratio continues 

 throughout the thermometric scale. Whether air at an average hio-h 

 temperature, like that in Florida, will contain this excess of moisture, 

 depends only on the proximity of water whence the vapor may he 

 obtained. 



The figures of relative humidity recorded by the Signal Service at 

 Jacksonville only indicate the ratio in per cent which the humidity of 

 the air at the time bears to saturated air at the same temperature. 

 But the weight of vapor in saturated air at that temperature is not 

 given, therefore the absolute value of this percentage, so far as the 

 records are concerned, is unknown. The basis for the calculation is, 

 however, easily obtainable the weight of vapor in troy grains, con- 

 tained in saturated air at different temperatures (Glaisher's Table) 

 and will be found to increase in an ascending scale from zero. The 

 following record of the Signal Service in Cincinnati, Ohio (Sergeant 

 R. B. Watkins, U. S. A., observer), well illustrates the subject : 



TEMPERATURE AND HUMIDITY. 



January 1, 1881 : 



Thermometer, degrees Fahr. . . . 

 Relative humidity, per cent. . . . 

 Actual humidity, grains 



June 1, 1881 : 



Thermometer, degrees Fahr.. . . 

 Relative humidity, per cent. . . . 

 Actual humidity, grains 



Average. 



21-8 

 71-5 

 1-08 



74-8 

 67-1 

 6-25 



From the above table we see that on a day of high temperature 

 and low relative humidity there was nearly six times more vapor in 

 the air than on a day of low temperature and high relative humidity. 



By way of comparison we here insert a table showing the mean 

 annual and winter temperature, also the relative humidity and abso- 

 lute humidity, of three winter stations. It shows the average quantity 

 of vapor in the air at Jacksonville, throughout the year, to be twice 

 as great as at St. Paul, Minnesota, and four times more during the 

 winter season : 



* The temperature of these places is from the " Smithsonian Temperature Tables." 

 The relative humidity is calculated from data of five years 1877-1881 inclusive sup- 

 plied the writer by the Chief Signal-Officer, General W. B. llazen, Washington, D. C. 



