One set, the convex curves, is for the determination of relative humidity of wet-and-dry-bulb hygrometer or psychrometer; the other, the concave curves, is derived from the vapor pressures and shows the amount of moisture per cubic foot at relative humidities and temperatures when read at the dew-point.
"Seasoning of Wood"
Joseph B. Wagner
The sling psychrometer as used by the U.S. Weather Bureau should, in the hands of an expert, give results making possible measurements accurate to two or three per cent.
"The Dollar Hen"
Milo M. Hastings
Moreover the degree of humidity at the place where there can be a question of setting up a psychrometer and hygrometer during a wintering in the high north, has not the meteorological importance which has often been ascribed to it.
"The Voyage of the Vega round Asia and Europe, Volume I and Volume II"
A.E. Nordenskieold