If the dry skin of one's finger is moved gently over a smooth metal surface covered with a thin insulating layer, and the metal is connected to the ungrounded side of a 110-v powerline, the surface has a characteristic feeling that disappears when the alternating voltage is disconnected. It is the purpose of this note to describe some observations concerning this effect and to suggest an explanation which may be of some interest, particularlyto those who have experienced the effect without realizing its cause. In the summer of 1950, E. Mallinckrodt noted that a certain shiny brass electric light socket did not feel as smooth when the light was burning as it did with the light off. It was soon discovered that when the light was turned on with the socket key, the socket was connected to the livewire (presumably because of imperfect insulation). If one reversed the plug in the floor receptacle the sensation ceased because the socket was then connected with the ground instead of the live side of the line, and there was no possibility of current flowing through one's body. The sensation was slight but definite when current (which later proved exceedingly minute) was flowing, and can best be described as a lack of smoothness or a feeling of vibration as one passes his fingers gently over the surface, such as might be caused by a small amount of resin. The sensation was considerably diminished if one changed fromleather to rubber-soled shoes, and increased if one moved his stockinged foot from the high-resistance wooden floor to the brick of the fireplace which extended into the ground. The effect was then noted in varying degrees (and confirmed by other observers) in a wide variety of objects when connected to the live wire and stroked with the fingers: for example, a lightly varnished brass door knob, an ordinary lacquered beer can, an egg in an electric egg boiler as the steam dried off. The hands of some individuals are more sensitive than others, and different parts of the hand yield different responses. Breathing upon the skin diminishes its sensitivity temporarily.

In an experinient made to investigate the effect quantitatively, an aluminum plate was connected to the ungrounded side of the 60-cycle, 110-v power supply through a variable current-limiting resistance. Half of the plate was coated with a very thin layer of an insulating varnish (Krylon). A man, standing on a Lucite insulator, touched the aluminum plate with one hand while the other was grounded through a meter by which the current passing through him could be measured. On drawing his finger lightly across the thinly varnished part of the plate, the peculiar resin-like sensation was felt. No such effect was observed when the finger was drawn in the same man-ner across the unvarnished part of the metal plate. With the highest current-limiting resistance used (22 megohms) the current through the man was about 1 Ramp when the finger was drawn across the var-nished part and the sensation was felt. It was 4 ytamp on the unvarnished part, and no sensation was felt. The effect was also perceived on an insulated surface when the observer's body was completely insulated from ground, and all the alternating current that flowed (less than 10-7 amp) did so by way of body to ground capacitance. The effect diminished as the ob-server moved farther from the floor on a ladder. No effect whatever was obtained with direct current. These data suggested that the effect was not due to direct actionof current on the sense organs. If, instead of the finger, the thinner skin of the nose is touched to the uninsulated part of the plate and the series resistance made small enough, an intermittent sharp pricking can be felt. This is direct …