In a message dated 7/18/00 1:36:18 PM Eastern Daylight Time, 
mlamb1@.......... writes:

<< I note that the Forcefield/Wondermagnet web site has a
 relatively big (6" length, 1" width by 1/2" thick) ceramic
 (ferrite) magnet for sale for U.S. $5.50 each.  800 gauss.
 The flat surface maybe easier to work with than a round
 rod.  Whether or not they are adequate for this application
 I don't know.  I'd question whether a series of neodymium
 magnets could be better or worse than a item like this in
 comparison trials.  One might even add on a neo or two on
 the ends of this, and see if it helps the sensitivity aspect?  See:
 
 http://www.wondermagnet.com/dev/magnet26.html
 
 Meredtih Lamb
  >>
Hi Meredith,
    I now realize, thanks to Chris Chapman, that using the Neodymium magnets 
from Wondermagnet was a mistake. Their temperature coefficient is very 
unfavorable compared to the Alnico magnets from Edmund Scientific that we 
have been using for many years to build McWilliams torsion balanced 
magnetometers. I am switching back to Alnico magnets which, although weaker, 
nevertheless provide adequate sensitivity.
    There was a very nice magnetic storm on 8 June that was very well 
recorded with  homemade torsion balance magnetometers. The June Solar 
Bulletin shows how well these recordings compare to nearby US Geological 
Survey Magnetic Observatory magnetograms made with a professional fluxgate 
magnetometer. The June Solar Bulletin also has complete details on how to 
build your own homemade fluxgate magnetometer for about US$ 40. There is a 
schematic and parts list and four pages of interesting information on how the 
fluxgate works. If anyone would like to have a free copy of this Bulletin 
please send me a self addressed stamped envelope (no stamps if outside USA) 
at the address below.
Best regards,

Casper H. Hossfield
PO Box 23
New Milford, NY 10959
USA
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