Abstract: Apparatus including a superconducting magnetic assembly for inducing nuclear magnetic resonance within a flowing medium. In order to make nuclear magnetic resonance measurements on a flowing medium it is preferred to have separate polarizing and resonating fields situated consecutively along the flow path, with the magnetic flux density in the resonating region being reduced from that in the previous polarizing region.The signal to noise ratio in such a system is improved by increasing the magnetic flux density in the polarizing region as much as possible. Using superconducting coils to provide the magnetic fields a lighter assembly with increased polarizing field strength over that of an equivalent iron-cored electromagnet is obtained.

Abstract: A coil for the production of homogeneous magnetic fields; the coil sides are disposed in sets of four arranged symmetrically about a common axis to which the coil sides are parallel. There are 2n turns of the coil and the disposition of coil sides is such that the n sums, each of which is the sum of 2n turns respectively of the quantities cos 3.psi..mu./R.sup.3 .mu., cos 5.psi..mu./R.sup.5 .mu. etc to cos (2n+1).psi..mu./R.sup.2n+1 .mu. are all substantially zero on the supposition that equal currents flow through all the turns of the coil. The equality to zero need not be exact, variation of up to 10.degree. in the angles for invariant R or variation of up to 10% in the various R.mu. for invariant angles .psi..mu. being tolerable. The coil (1.ltoreq..mu..ltoreq.n) is particularly intended for use in the measurement of the properties of liquid media by determinations of nuclear resonance.