Re: What is the history and science behind 'weather sticks' what kind of wood?

There seems to be little information on the working of the weatherstick, 
other than that it appears to work as claimed. The only source I was able to 
locate which was anything more than a sales pitch for the product was an 
article in the Diwan Magazine

 http://www.datadiwan.de/magazin/index_e.htm?/magazin/
dz0108e_.htm

which describes an experiment conducted on the weatherstick to determine 
which weather factors affected it. Once you get past all the fringe science 
stuff, you'll find the results of an experiment in which a weatherstick was 
placed beneath an overhang to protect it from direct precipitation, while 
allowing it to be affected by all other atmospheric conditions. Measurements 
of the amount of light, the air temperature, and the relative humidity were 
taken over a two-week period, and the only significant factor in the bending 
of the stick appeared to be relative humidity. 

This seems to me to be part of the explanation; there is no question that 
dampness causes wood to twist or warp. From the information I was able to 
find, the wood used is from a tree whose branches differ in composition 
between the top and bottom of the branch. Differential swelling is what 
causes the branch to bend - under certain conditions, the top of the branch 
will swell to a different degree than the bottom, forcing the branch to bend 
in an arc with the less swollen part of the branch on the inside of the arc. 
Changes in relative humidity could certainly account for this. 

However, there is no indication in the report of any consideration of a 
relationship between barometric pressure and bending. I believe this to be 
an experimental oversight, since a change in local relative humidity is not 
necessarily a sign of weather change, and even when it is, the change in RH 
occurs with the onset of the change, not prior to it. And given that the RH 
can change on an hourly basis simply with daytime warming or cooling of the 
air, it seems odd that the weatherstick would not respond to this.

What =does= consistently change prior to the arrival of a weather system is 
the barometric pressure. As a low pressure area, which brings cool, moist 
air, approaches, the barometer falls. Conversely, it rises with the approach 
of a high pressure area, which brings dry air. Wood, as the product of a 
living organism, is made of cells. In green wood, these cells are filled 
with liquid. In dry wood, however, the cells have lost their moisture, 
shrunk, and left air pockets between them. (That's why a dry piece of wood 
is much lighter than a green or a waterlogged piece.) If there is a 
difference in density between the two parts of a weatherstick, it is 
entirely conceivable that the stick could be acting as an aneroid barometer. 
That is to say, as the air pressure rises and falls, the less dense portion 
of the branch will shrink or expand to a greater degree than the denser 
portion, forcing the branch to bend. If such an effect actually takes place, 
the weather stick would respond to approaching weather changes with a higher 
degree of accuracy than simple relative humidity would account for.

But, given the lack of information regarding the compositional difference 
between the two parts of the branch, this is simple speculation on my part. 

As for the history of the stick, all I was able to ascertain was what 
appears on the website to which you pointed in your question, namely that 
the local Abanaki Indians noticed this phenomenon a long time ago, and 
utilized it to make near-term predictions of weather change.

Whatever the cause, the weather stick seems to be a genuine indicator of 
changing weather, and beats the weather rock ("Touch the rock. If it's dry, 
it's not raining. If it's wet, it's raining.") as a natural predictor of 
weather.

Thanks for a great question!

Denni