The relative humidity is a factor that we always need to take into consideration
during any investigation, but how many people understand why this is so important?

As investigators we need to be aware of a few important facts about this
atmospheric condition:

• Humidity is the level of moisture in the atmosphere.
• Air at a particular temperature can hold only so much moisture.
• Air holding the maximum amount of moisture possible is said to be saturated.
• Humidity is measured as a percentage of moisture content within the
  atmosphere - complete saturation is measured at 100%RH.
• Warmer air can hold a lot more moisture than cooler air.
• Raising the air temperature by 9°C doubles its moisture capacity.
  This means that air at 30°C can hold 8 times as much moisture than it would at 3°C.
• If we cool the air without changing its moisture content the relative humidity will
  rise until eventually we'll reach a temperature at which saturation occurs.
• When saturation occurs, the air can no longer contain its moisture - this is known
  as the dew point.
• As saturation occurs when the dew point temperature and air temperature are equal, the dew point temperature can never be greater than the air temperature.
• When the dew point is reached moisture must be removed from the air, this is accomplished through condensation. This process results in the formation of tiny water droplets that can lead to the development of fog, frost, clouds, or even precipitation such as dew or rain.


Any substance that holds moisture is governed by the phenomena noted above including rivers, earth, trees, plants, even you and I. When we breathe out in colder climates, the breath cools almost immediately causing the saturation point to be reached quickly and the moisture is dispersed from our breaths causing a mist.

On a grander scale this is what causes mist and fog during Spring and Fall.

Paranormal investigators must take into consideration this phenomena as it can be easily confused with reported activity such as spectral mists as the following photograph illustrates.

This photograph was taken in a large hall in February 2006. The temperature was measured at 1°C.

Orbs are another favourite phenomena confused by the achievement of the atmospheric dew point. As saturation occurs and the air begins to loose its moisture, water particles and droplets are present in the air. When we take a photograph, the flash from our cameras illuminate theses droplets. These, to the untrained investigator become orbs as the following photograph illustrates.

Humidity is measured by the aid of a hygrometer. This device samples the air and calculates the percentage of moisture in the air dependant on the temperature at the time.

CaSPIR use two types of hygrometer during our investigations, these are.

'4-in-1' Environmental Multi-Meter (ST-8820)

This meter is a must for all investigations!
Although bulkier than any single piece of equipment, this instrument does the work of 4 instruments, one of which being a hygrometer.
The accuracy of this meter is well within the limits of comparable individual meters so there is no loss of quality in the readings.

EL-USB-2 Datalogger.

A datalogger does exactly what the name suggests - it logs data!

There are various models made by Lascar but this version samples the air from its surrounding environment and automatically records the temperature and relative humidity at specified intervals.


As this tool samples automatically, it is ideally suited to a locked-off environment.

To set the time between samples (along with the start and end time) the investigator unfortunately requires access to a PC (MAC is not supported by the datalogger's software).

The software also allows the investigator to view the readings as a line-graph clearly showing the levels (vertical axis) against the time (horizontal axis) which can be easily included in investigation reports. See the sample below!

An example of a graph plotted by EL-USB-2's software.

Both these items are available from 'Parascience Shop' or 'Tom's Gadgets'.

© County Society for Paranormal Investigation and Research - 2008

 

Last Updated 27/07/2008