76 NEGRETTI AND ZAMBEA, HOLBORN VIADUCT, E.G., 



101. For practical purposes in estimating the comparative humidity, the 

 annexed table, which is a reduction from Mr. Glaisher's elaborate work, will 

 be sufficient. 



The total quantity of aqueous vapour which at any temperature can be 

 diffused in the air being represented by 100, the percentage of vapour actually 

 present will be found in the table opposite the temperature of the dry-bulb 

 thermometer, and under the difference between the dry-bulb and the wet-bulb 

 temperatures. The degree of humidity for intermediate temperatures and 

 differences to those given in the table can be easily estimated sufficiently 

 accurately for most practical purposes.* 



This table will be found serviceable to Horticultarists, since it will enable 

 them to estimate the chilling effect of dew or hoar-frost on tender plants. 



In England the usual difference between the thermometer readings, in 

 the open air, shaded from the sun, reflected heat, and currents of air, ranges 

 from one to twelve degrees. In hot and dry climates, as India and Australia, 

 the range out of doors has been found as much as 30. 



A. still more comprehensive but simple Dew-Point or Humidity Table has been recently published 

 by William Marriott, Esq., F.M.S., price 6d. 



