Martin McCormick writes:

<<  I don't have any figures on the coefficient of Tungsten or the other
 parameters of the bulbs, but I wondered if I was seeing true temperature
 variations or just a dirty socket on one of the bulbs.  When we got another
 60 DG day, the resistance did go back up to around 69 or 70 Ohms.
  >>

Tungsten:  at 20 degrees C, alpha = .0045; at 1000 degrees C, alpha = .0089
Copper, hard drawn: at 20 degrees C, alpha = .00382

These from Handbook of Chemistry and Physics, 39th edition, Chemical Rubber
Publishing Co.

I never realized tempcos were so high!  Means that you should have observed a
resistance change on the order of eight ohms or so.

Regards,
Shel Michaels
Massachusetts, USA