Prof. Riess on Electric Pauses. 263 



The arrangement of the electricity upon the surface of the 

 sphere, produced by the approximation of the cone, is to be 

 regarded as the primary cause of the plifenomenon under consi- 

 deration. It is known that by the proximity of a conductor 

 connected with the earth, the electric arrangement in an elec- 

 trified body is essentially changed ; so that, theoretically con- 

 sidered, a point of an electrified sphere, for example, may, by the 

 approximation of one unelectrified, be made to assume any den- 

 sity whatever. When the cone connected with the earth is caused 

 to approach the sphere in the above experiments, the nearest 

 point of the sphere assumes the greatest electric density, and 

 from this point all round the density diminishes vipon the sur- 

 face of the sphere, according to a certain law. Let us fix our 

 attention upon the convex surface of a small segment of the 

 sphere {kuppe, calotte), on which the density is not less than 

 that which is necessary to cause the electricity to stream out- 

 wards. The density at the highest point, and also the size of this 

 segment depend on the shape and the relative magnitudes of the 

 sphere and cone, and also on their distance asunder. If the 

 cone were a thin sharp point, the density upon the nearest point 

 (9 lines distant) of the sphere must be very great ; but the mag- 

 nitude of the superficial segment alluded to must be very small, 

 inasmuch as M. Riess could observe no hght upon the sphere, 

 although the conductor at the same time was losing the greater 

 portion of its electricity. When, on the contrary, the frustum 

 made use of in the experiment stood near the sphere, the density 

 at the highest point of the spherical segment was not very great 

 in comparison with the mean density of the sphere, a fact esta- 

 blished by experiment with the torsion balance. The size of the 

 segment must, however, have been considerable, as it appeared 

 luminous on being electrified by the machine. While the den- 

 sity of the segment became smaller as the distance of the cone 

 from the sphere was augmented, the greatest breadth of the lumi- 

 nous segment (i an inch) was found by M. Riess, not at the 

 smallest distance' of the electrodes (9 lines), but at a distance of 

 an inch and a half. This arrangement of the electricity on the 

 sphere gives the explanation of the pause phsenomenon. By the 

 continuous action of the machine, the sphere receives from the 

 conductor a definite amount of electricity in a certain time, and 

 with it a density sufticient for a spark 4 inches in length. If 

 during this time the quantity of electricity delivered by the ma- 

 chine be diminished by streaming into the air, then the density 

 imparted to the sphere suffices only for sparks of less length. 

 The streaming out takes place at all ])oints of the sphere where 

 the density exceeds a certain value, and is the more active the 

 greater is the density. If a sharp metallic point be brought 



