The Long-Period Telluric Instrument (LTI) LEMI-420E is developed for telluric field measurements – signals with periods of 20…100.000 seconds are recorded with very high sensitivity and low drift. In order to realize such design major attention was paid to thermal and temporal stability, high input impedance and low drift of electric channels. High-pass filter-free technology of input stages was used in order to let super-long period signals to pass. The lightning protection unit allows both the protection against nearby lightning discharges and easy connection of electric lines in the field. There are four electric channels in the instrument for measurements additionally of vertical component of telluric field or the components along some local geological structure. Specially developed very low noise LEMI-701 electrodes are recommended (at the photo, right), but any other electrode types may be used too.