Dowsing, water divining or water-witching, is an ancient skill, not fully understood by orthodox science, in which gifted individuals are able to locate underground water (or indeed any object, pipe, tunnel, cable, mineral vein, etc.) by means of a neurophysical response when passing over the target object. The muscular spasm induced in the process is usually, but not always, amplified by the use of a dowsing instrument or rod. These come in many forms; most commonly, the forked hazel twig, the modern equivalent (two knitting needles with their points driven into a cork), the pendulum (a weight on the end of a string), L-rods (fashioned from two wire coat hangers) and so on. Most good dowsers search for 'tangible targets'. These would be as described above and the efficiency of the dowser can be tested by digging to verify that the search has been successful. The ability to find water and minerals, the outline of buried foundations and pits is well documented and accepted, if not fully understood. More recently people are claiming to be able to locate 'intangible targets' or to be able to dowse from a map. Growing interest in earth mysteries in the 1970s led to the development of the theory that ancient sacred sites were located to mark or control the flow of a subtle 'earth energy' or 'life force' which they believe was an important part of a cosmic/sacred engineering system in the ancient past (the Golden Age). This belief, in part came from the writings of Guy Underwood in the 1950s (not published until the late 1960s) and was developed by other dowsers, particularly Tom Graves, who theorised about ancient standing stones and 'earth acupuncture' and fostered the belief in 'energy dowsing'. Attempts to measure such energies have been unsuccessful.