We study fluctuations of conductance of two connected in series dots in the
Coulomb blockade regime. The pattern of the fluctuations turns out to be e
xtremely sensitive to a magnetic field. These conductance fluctuations also
provide information about the mesoscopic fluctuations of charge of a parti
ally opened single quantum dot, which are hard to measure directly. [S0163-
1829(99)07115-5].