1. A method of non-destructively identifying and assaying the make-up of a test object by comparison with a statistical record of a plurality of similar known objects by use of a capacitance sensor having a pair of parallel plates which have an adjustable spacing therebetween which can be established at accurately known intervals, and at least a first of the plates being configured as an array of independent plate segments which can be selectively employed, each of the segments being coupled to respective means to sense a current thereat at an accurately measured phase and frequency, the method comprising the steps of placing said test object between said parallel plates, accurately adjusting the spacing between said plates to correspond with a thickness dimension of the object, and selecting the appropriate ones of said segments to correspond with a cross section of the object; applying a plurality of sinusoidal voltages each of an accurately known amplitude, frequency, and phase, to the other plate of said capacitive sensor; accurately measuring magnitudes and phases of the electric currents in each of said selected segments of the first of the plates for the applied sinusoidal voltage of each said frequency; from said measured electric current magnitudes and phases, calculating one or more parameters including at least one of the capacitance, conductance, frequency dependence of capacitance, and frequency dependence of conductance for said test object; and comparing said calculated parameters for the test object with stored values that represent a statistically normal range of such parameters that characterize a plurality of known objects similar to said test object.