A technique in which a very high voltage (30 000–50 000 volts) creates a high intensity electric field which can be recorded on a photographic plate as a form of electrical interference. The phenomenon was discovered by Russian engineer Semyon Kirlian and his wife Valentina during the 1950s. Materials which are good conductors give an image of the surface of the object; poor conductors show detail of their inner structure. Dead objects have a constant image, whereas living objects show a constantly changing pattern, which in human beings is said to correspond to the aura and to reflect the physical and psychological state of the subject. There is now research interest into the electrical interference patterns associated with normal and diseased tissue, including cancer cells. Computer evaluation of these patterns may, in the future, form the basis of a new system of tissue diagnosis.