We present new results of a survey for weak magnetic fields among DA white dwarfs with inclusion of some brighter hot subdwarf stars .
We have detected variable circular polarization in the H \alpha line of the hot subdwarf star Feige 34 ( SP : sdO ) .
From these data , we estimate that the longitudinal magnetic field of this star varies from -1.1 \pm 3.2 kG to +9.6 \pm 2.6 kG , with a mean of about +5 kG and a period longer than 2 h. In this study , we also confirm the magnetic nature of white dwarf WD1105-048 , found earlier in a study by Aznar Cuadrado et al .
( 4 ) , and present upper limits of kilogauss longitudinal magnetic fields of 5 brightest DA white dwarfs .
Our data support the finding of Aznar Cuadrado et al .
( 4 ) that \sim 25 % of white dwarfs have kilogauss magnetic fields .
This frequency also confirms results of early estimates obtained using the magnetic field function of white dwarfs ( 7 ) .