Abstract: An electromagnetic survey system for geophysical exploration comprising a reconnaissance method and a survey line method. The reconnaissance method finds the principal electrical axis of conductivity of anomalous zones of conductivity by measurement of variations in the earth's magnetic field in a grid pattern over the survey area, calculation of Tipper vectors for each site, and plotting the vectors to scale. The conductivity axis is determined as being perpendicular to a set of the largest parallel vectors, one or more of which reverse direction, and passing between the direction reversal. A Survey line may be collimated with the set of enlarged vectors to make three dimensional effects more symmetrical so they are attenuated.

Abstract: A sample is analyzed for the presence of an element by exposing it to radiation which causes the element to emit a characteristic radiation. Background radiation and the characteristic radiation are passed through a first filter which attenuates the characteristic radiation. The time required for a fixed amount of radiation to pass through the first filter is measured to establish a reference time. Radiation from the sample is then passed through a second filter which attenuates the characteristic radiation by an amount different from the first filter. The amount of radiation passing through the second filter is measured during a time interval substantially equal to the reference time. The difference between the two amounts of radiation indicates the amount of element in the sample and reduces errors due to samples of different composition and physical condition and due to variation of radiation intensity from the source.