# Relative Humidity

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```					            Measuring Relative Humidity
Relative Humidity is a measure of the amount of moisture in the air. It is normally expressed as a
percentage, however in fixed temperature instances such as incubators, it is sometimes simply
expressed as the ‘Wet Bulb Reading’ or the ‘Wet Bulb Depression’ .

Humidity is important in the incubation of eggs. Too little humidity, and the egg loses moisture
causing failure at hatching, or if severe, premature death of the embryo. Too much humidity and
the chicks can develop deformities and hatch with unhealed navels.

Relative Humidity can be simply measured in the classroom.

You need:

Two Thermometers
Bowl of water
Length of shoelace (hollow type)
Rubber Band
Relative Humidity Chart

Method

Thread the shoelace over the bulb of one thermometer and fix with the rubber band.

Place the other end of the shoelace in the water bowl and notice the water travel up the
shoelace to the bulb.

The temperature of this ‘wet bulb’ thermometer will lower.

Subtract this reading from the dry bulb
temperature to obtain the Temperature
Difference

Use the Relative Humidity Chart to calculate
the actual Relative Humidity.

Take readings on different days and during
different weather conditions and notice the                  Therm1
differences in humidity.
Relative Humidity Chart
To Calculate Relative Humidity

Read the Dry Bulb Temperature along the vertical rows. Read the difference between Dry & Wet
Bulb temperatures along the top Column. The intersection of these two figures indicates the
Relative Humidity expressed as a Percentage.
Difference between Dry & Wet Bulbs – Degrees Celsius

1   2   3   4   5   6   7   8   9 10 11 12 13 14 15 16
10 88 77 65 54 44 34 24 14 5
11 88 77 66 56 46 36 26 17 8
12 89 78 68 57 48 38 29 20 11 3
13 89 79 69 59 49 40 31 23 14 6
14 90 79 70 60 51 42 33 25 17 9         2
Air Temperature – Degrees Celsius (Dry Bulb)

15 90 80 71 61 52 44 36 27 20 12 5
16 90 81 71 62 54 46 37 30 22 15 8          1
17 90 81 72 64 55 47 39 32 24 17 10 4
18 91 82 73 65 56 49 41 34 27 20 13 7
19 91 82 74 65 58 50 43 35 29 22 15 9           3
20 91 83 74 66 59 51 44 37 30 24 18 12 6
21 91 83 75 67 60 52 46 39 32 26 20 14 8            3
22 96 83 76 68 61 54 47 40 36 30 22 16 11 5
23 96 84 76 69 62 55 48 42 36 30 24 18 13 8             3
24 96 84 77 69 62 56 49 43 37 31 26 21 15 10 5
25 96 84 77 70 63 57 50 44 38 33 27 22 17 12 7              3
26 96 85 78 71 64 58 51 46 40 34 29 24 19 14 9              5
27 96 85 78 71 65 59 52 47 41 36 30 25 21 16 11 7
28 96 85 79 72 65 59 53 48 42 37 32 27 22 18 13 9
29 96 86 79 72 66 60 54 49 43 38 33 28 24 19 15 11
30 96 86 79 73 67 61 55 50 44 39 34 30 25 21 17 13
31 96 86 80 73 67 62 56 51 45 41 36 31 27 22 18 14
32 97 86 80 74 68 62 57 52 46 42 37 32 28 24 20 16
33 97 86 80 74 69 63 58 52 47 43 38 34 29 25 21 17
34 97 86 81 75 69 64 58 53 48 44 39 35 30 26 23 19
35 97 87 81 75 70 64 59 54 49 44 40 36 32 28 24 20
36 97 87 81 76 70 65 60 55 50 45 41 37 33 29 25 21
37 97 87 82 76 70 65 60 55 51 46 42 38 34 30 26 23
38 97 88 82 76 71 66 61 56 51 47 43 39 35 31 27 24
39 97 88 82 77 71 66 61 57 52 48 44 40 36 32 28 25
40 97 88 82 77 72 67 62 57 53 48 44 40 37 33 29 26

```
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Description: Relative Humidity