  Using coherence analysis (which is an extensively used method to study the
correlations in frequency domain, between two simultaneously measured signals)
we estimate the time delay between two signals. This method is suitable for
time delay estimation of narrow band coherence signals for which the
conventional methods cannot be reliably applied. We show by analysing coupled
R\"ossler attractors with a known delay, that the method yields satisfactory
results. Then, we apply this method to human pathologic tremor. The delay
between simultaneously measured traces of Electroencephalogram (EEG) and
Electromyogram (EMG) data of subjects with essential hand tremor is calculated.
We find that there is a delay of 11-27 milli-seconds ($ms$) between the tremor
correlated parts (cortex) of the brain (EEG) and the trembling hand (EMG) which
is in agreement with the experimentally observed delay value of 15 $ms$ for the
cortico-muscular conduction time. By surrogate analysis we calculate error-bars
of the estimated delay.
