STATIC—about which much is said and very little is, as a rule, understood. When meters burn out or tubes puncture, or the patient is “shocked,” the trouble is generally, and often correctly, diagnosed as static, but even after the trouble has been correctly classified, most roentgenologists seem to be at a loss as to what steps should be taken to correct it. To the minds of most doctors the word “static” would suggest the word “ground,” but too often the object of grounding a piece of apparatus and the principles involved are imperfectly understood. The primary reason for grounding the various pieces of X-ray apparatus is the protection of the operator and the patient. For instance, should the masts of a tilt table “break down” while the frame of the table is grounded, the greatest trouble is likely to be the burning out of a fuse or the opening of a circuit breaker. If, however, the frame were not grounded and the patient or operator stood in the path between it and some grounded conductor, his body would complete the circuit and thereby receive a severe shock. The second reason for grounding all parts of the apparatus and also for the use of static shunts is in order to dissipate static electricity as it is accumulated. Take, for example, a dam in a small mountain stream. As long as there is a large outlet at the bottom there is no pressure against the dam. The smaller this outlet is made the higher the pressure will rise until, if there is a weak spot in the dam, it breaks. To a certain extent this is similar to the conditions that arise when a conductor is placed in an electro-static field. If the resistance to the ground is very low there is little chance for the amount of the static electricity to become large enough to do any damage, but as the resistance increases the charge on the conductor increases, up to certain limits. That is to say that, especially in the vicinity of deep therapy apparatus and where trouble with static has been experienced, this trouble can be reduced by using large wire in the grounding circuit, making electrically secure joints, and attaching the ground clamps securely to the water pipe as close as possible to where this pipe enters the building. If one of the service wires is grounded, this should also be used. The use of static shunts to protect the wiring of the apparatus and the instruments from damage due to static electricity is now a standard practice. The shunts are of a comparatively high resistance in order that no appreciable amount of the 110 or 220 volt circuit can leak to the ground, but are of low enough resistance to dissipate the static that is accumulated before it might attain any harmful proportions. It should be remembered that any conductor that is surrounded by a grounded conductor cannot be appreciably affected by any electrostatic field from the outside.