Dean S. Messing wrote:
John Summerfield wrote:
owerful "undo" features of emacs. Solution: thumbs up!
:
: Touchpads are misnamed; they don't require touch. There's some kind of
: proximity detector involved.
I believe it is a capacitive sensor and depends on the Dielectric
Constant of the material between the pad and one's finger. I just did
several little experiments to check. (I'm a scientist, after all :-)
grumble grumble[1]
First, I took my finger and put it really close to the pad w/o
touching it. No cursor motion. (Air has a small dielectric constant.)
Then I took a thin piece of paper and tried to move the cursor by
sliding finger over paper. No go unless I pressed very hard. Paper
is pretty incompressible so I don't think it was that my finger was
getting closer. Rather the surface area of the contact was increasing
so the capacitive effect was greater the harder I pressed.
Interestingly, through a much thicker envelope glue label, my finger
had no trouble moving the cursor at normal pressure. My guess is that
the glue in between the label and the backing has a high
Dielec. Const.
Finally, I used my finger nail. Being an insulator, it had no effect
even pressing hard.
I previously test on a G4 17" powerbook running OS X (I don't recall
whether Panther or Tiger). I could move the cursor without touching the
touchpad.
Now I have a G4 15" powerbook running Tiger. I can (just) touch the
touchpad, sliding across the surface with my finger, not moving the cursor.
Non-ferrous metals seem to work much the same as fingers. Side of SATA
cable works. Plastics (polystyrene packaging, Faber-Castell fluoro pen)
and cardboard don't work. Neither does some insulated wire (about the
size of wirewrap wire).
[1]
Daughter was a (just-graduated) scientist, working as a Research
Assistant on a project involving Alzheimer's at http://www.mhri.edu.au.
The lead got his Ph D, the grant ran out and she needed a job. She got
one, doing data entry for an insurance company. She's doing well for
herself in insurance (she talks to the board), but I wish the country
paid its scientists well, we need science more than we need good
insurance professionals.
--
Cheers
John
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