HIGH FREQUENCY AND HIGH POTENTIAL CURRENTS. 131

ducting electrode, even if the latter be of aluminum, the brushhas only a very short existence, but it can be preserved for a con-siderable length of time in a bulb devoid of any conducting elec-trode. To observe the phenomenon it is found best to employ alarge spherical bulb having in its centre a small bulb supportedon a tube sealed to the neck of the former. The large bulb be-ing exhausted to a high degree, and the inside of the small bulbbeing connected to one of the terminals of the coil, under certainconditions there appears a misty haze around the small bulb,which, after passing through some stages, assumes the form of abrush, generally at right angles to the tube supporting the smallbulb. When the brush assumes this form it may be brought toa state of extreme sensitiveness to electrostatic and magnetic in-fluence. The bulb hanging straight down, and all objects beingremote from it, the approach of the observer within a few paceswill cause the brush to fly to the opposite side, and if he "walksaround the bulb it will always keep on the opposite side. It maybegin to spin around the terminal long before it reaches that sen-sitive stage. When it begins to turn around, principally, butalso before, it is affected by a magnet, and at a certain stage it issusceptible to magnetic influence to an astonishing degree. Asmall permanent magnet, with its poles at a distance of no morethan two centimetres will affect it visibly at a distance of two me-tres, slowing down or accelerating the rotation according to howit is held relatively to the brush.

When the bulb hangs wdtli the globe down, the rotation is al-ways clockwise. In the southern hemisphere it would occur inthe opposite direction, and on the (magnetic) equator the brushshould not turn at all. The rotation may be reversed by a mag-net kept at some distance. The brush rotates best, seemingly,wdien it is at right angles to the lines of force of the earth. Itvery likely rotates, wdien at its maximum speed, in synchronismwith the alternations, say, 10,000 times a second. The rotationcan be slowed down or accelerated by the approach or recessionof the observer, or any conducting body, but. it cannot be re-versed by putting the bulb in any position. 'Very curious experi-ments may be performed wdtli the brush when in its most sensi-tive state. For instance, the brush resting in one position, theexperimenter may, by selecting a proper position, approach thehand at a certain considerable distance to the bulb, and he maycause the brush to pass oft by merely stiffening the muscles of