Well logging

Claim 1

IN A SYSTEM FOR SEISMIC MEASUREMENTS, SURFACE APPARATUS COMPRISING A RECORDING UNIT, SUBSURFACE APPARATUS ADAPTED TO BE LOWERED INTO A BOREHOLE, MEANS SUPPORTING SAID SUBSURFACE APPARATUS IN SAID BOREHOLE, SAID SUBSURFACE APPARATUS COMPRISING AN ACOUSTIC WAVE SOURCE AND TWO RECEIVERS SPACED FROM EACH OTHER ALONG A VERTICAL LINE, SAID RECEIVERS BEING MOUNTED TO ONE SIDE OF SAID WAVE SOURCE, A SINGLE ELECTRIC CIRCUIT MEANS CONNECTING BOTH SAID RECEIVERS TO SAID RECORDING UNIT, MEANS FOR ENERGIZING SAID WAVE SOURCE TO PRODUCE AN ACOUSTIC IMPLUSE REACHING SAID TWO RECEIVERS IN SUCCESSION, MEANS IN EACH RECEIVER FOR TRANSLATING EACH RECEIVED IMPULSE INTO A SEPARATE SIGNAL RELATED TO THE IMPULSE TRAVEL TIME, SAID SEPARATE ELECTRICAL SIGNALS EACH BEING TRANSMITTED BY SAID CIRCUIT MEANS TO SAID RECORDING UNIT, AND SWITCHING MEANS IN SAID SUBSURFACE APPARATUS ACTUATED UPON THE PRODUCTION OF SAID ACOUSTIC IMPULSE FOR DISCONNECTING THE RECEIVER NEAREST TO SAID WAVE SOURCE FROM SAID CIRCUIT MEANS.