s with the
convex curve marked with the difference between the wet and
dry readings. The horizontal line passing through this
intersection will give the relative humidity.

Example: Dry bulb 70 deg., wet bulb 62 deg., difference 8 deg.. Find 70 deg.
on the horizontal line of temperature. Follow up the
vertical line from 70 deg. until it intersects with the convex
curve marked 8 deg.. The horizontal line passing through this
intersection shows the relative humidity to be 64 per cent.

EXAMPLE 2. To find how much water per cubic foot is
contained in the air:

Find the relative humidity as in example 1. Then the nearest
concave curve gives the weight of water in grains per cubic
foot when the air is cooled to the dew-point. Using the same
quantities as in example 1, this will be slightly more than
5 grains.

EXAMPLE 3. To find the amount of water required to saturate
air at a given temperature:

Find on the top line (100 per cent humidity) the given
temperature; the concave curve intersecting at or near this
point gives the number of grains per cubic foot.
(Interpolate, if great accuracy is desired.)

EXAMPLE 4. To find the dew-point:

Obtain the relative humidity as in example 1. Then follow up
parallel to the nearest concave curve until the top
horizontal (indicating 100 per cent relative humidity) is
reached. The temperature on this horizontal line at the
point reached will be the dew-point.

Example: Dry bulb 70 deg., wet bulb 62 deg.. On the vertical line
for 70 deg. find the intersection with the hygrometer (convex)
curve for 8 deg.. This will be found at nearly 64 per cent
relative humidity. Then follow up parallel with the vapor
pressure (concave) curve marked 5 grains to its intersection
at the top of the chart with the 100 per cent humidity line.
This gives the dew-point as 57 deg..

EXAMPLE 5. To find the change in the relative humidity
produced by a change in temperature:

Example: The air at 70 deg. Fahr. is found to contain 64 per
cent humidity; what will be its relative humidity if heated
to 150 deg. Fahr.? Starting from the intersection of the
designated humidity and temperature coordinates, follow the
vapor-pressure curve (concave) until it intersects the 150 deg.
temperature ordinate.