Page:Journal of the American Society of Mechanical Engineers, Volume 33.pdf/654

Rh temperature. However, he was unable to establish the correctness of his assumptions, partly because the data then extant regarding the speciﬁc heat of air and the latent heat of water vapor were inaccurate, but more particularly because he assumed the temperature indicated by the stationary wet-bulb thermometer which he used, to be the true temperature of evaporation, while as a matter of fact, it is considerably higher, owing, as we have shown, to the effect of radiation upon the stationary wet bulb.

28The author ﬁrst observed that the wet-bulb temperature given in the psychrometric tables of the United States Weather Bureau agreed substantially with the computed temperature at which air of a known temperature and moisture content would become saturated adiabatically, i.e., without the addition or subtraction of heat. These calculations were made by the writer in 1903, in determining the moisture-absorbing capacity of air in connection with the fan systems of drying. Subsequently, this relationship was still further investigated and thoroughly established in connection with the system of air conditioning introduced by the writer.

29Tests upon progressive fan-system dry kilns in 1904 disclosed the fact that the wet-bulb temperature was substantially the same in all parts of the kiln regardless of the drop in temperature due to moisture absorption, a phenomenon which logically results from the identity of the wet-bulb temperature and the temperature of adiabatic saturation.

30The following principles underlie the entire theory of the evaporative method of moisture determination, as well as of air conditioning: