164

INVENTIONS OF NIKOLA TESLA.

greater power. When a small length of ordinary cotton coveredwire, Fig. 107, is attached to one terminal of the coil, the streamsissuing from all points of the wire may be so intense as to producea considerable light effect. When the potentials and frequenciesare very high, a wire insulated with gutta pei’cha or rubber andattached to one of the terminals, appears to be covered with aluminous film. A very thin bare wire when attached to a ter-minal emits powerful streams and vibrates continually to and froor spins in a circle, producing a singular effect (Fig. 108). Someof these experiments have been described by me in The ElectricalWorld , of February 21, 1891.

Another peculiarity of the rapidly alternating discharge of theinduction coil is its radically different behavior with respect topoints and rounded surfaces.

If a thick wire, provided with a ball at one end and with apoint at the other, be attached to the positive terminal of a staticmachine, practically all the charge will be lost through the point,on account of the enormously greater tension, dependent on theradius of curvature. But if such a wire is attached to one of theterminals of the induction coil, it will be observed that with veryhigh frequencies streams issue from the ball almost as copiouslyas from the point (Fig. 109).

It is hardly conceivable that we could produce such a condi-tion to an equal degree in a static machine, for the simple reason,that the tension increases as the square of the density, which inturn is proportional to the radius of curvature; hence, with asteady potential an enormous charge would be required to makestreams issue from a polished ball while it is connected with apoint. But with an induction coil the discharge of which alter-nates with great rapidity it is different. Here we have to dealwith two distinct tendencies. First, there is the tendency toescape which exists in a condition of rest, and which depends onthe radius of curvature; second, there is the tendency to dissi-pate into the surrounding air by condenser action, which de-pends on the surface. When one of these tendencies is a maxi-mum, the other is at a minimum. At the point the luminousstream is principally due to the air molecules coming bodily incontact with the point; they are attracted and repelled, chargedand discharged, and, their atomic charges being thus disturbed,vibrate and emit light waves. At the ball, on the contrary, thereis no doubt that the effect is to a great extent produced indue-