284 Messrs. J. Trowbridge, T. C. and I. C. Howe on the 



gap is small, a silent discharge lowers the difference of po- 

 tential between the spark-terminals. As the distance between 

 these terminals increases, the silent discharge diminishes ; 

 and the difference of potential increases until a point is 

 reached at which strong inductive effects take place between 

 all surrounding objects. The energy of the electrostatic 

 field thus manifests itself by what we may perhaps term 

 an ionization and electrical attraction and repulsion of the 

 particles of the air. This electrostatic action does not extend 

 to the great distances reached by the electromagnetic effect 

 of the field. While the latter can be detected many miles, the 

 electrostatic effect is confined to a few feet. Thus a spark of 

 6 or 7 feet in length (180 to 210 centims.) is vastly inferior 

 to one of 2 or 3 inches (5 to 7*5 centims.) for the purposes of 

 Avireless telegraphy. In experiments with electric waves by 

 means of coherers we found that the electrostatic effect was 

 very disturbing up to a distance of 20 feet from the spark- 

 tenninals when these terminals were (5 feet apart. The dis- 

 turbance diminished as the terminals were brought nearer 

 together. The minimum of the curve representing this disturb- 

 ance coincided with the minimum of the curve representing 

 the explosive effect. On the other hand, the action of the 

 magnetic waves on the coherer became regular beyond a 

 distance of about 20 feet. 



The electrostatic effect is evidently some function of the 

 electrical density on the terminals of the spark-gap and on 

 the coatings of the condenser. 



The following experiments illustrate this dependence of the 

 sparking-distance upon this density. A chronograph-cylinder 

 was provided with two pointers S and S' (fig. 3), one of which 

 was connected to one coating -p-^ 3 



of a condenser, C, while the 

 other coating of the condenser 

 was joined to the metal cylinder 

 of the chronograph. The coat- 

 ings of the condenser were 



charged through an adjustable (HI,. .7} CH * 



very large liquid resistance by 



means of ten thousand cells, B. The other pointer was con- 

 nected with one terminal of a small Ruhmkorf coil, I, while 

 the other terminal wire of the coil was led to the cylinder of 

 the chronograph. The primary of the Ruhmkorf coil was 

 interrupted by a seconds pendulum which broke the circuit 

 at S. The pointers were placed on a carriage. When this 

 was released, the pointers drew lines on blackened paper 

 (fig. 4) placed upon the chronograph-cylinder : and the 



