6 Trans. Acad. Sci. of St. Louis. 



glass midway between them, so that no disruptive dis- 

 charge may occur. The disk is to he in metallic connec- 

 tion with the negative terminal. A point of light emerges 

 from the pin-point or the pencil mark, and moves slowly 

 over the film, curving towards the positive terminal of 

 the machine, and leaving a darkened trail behind. Along 

 this trail an invisible negative flow is taking place, as can 

 be seen by bringing near to it a device which has earned 

 the name of "teazer." This consists of two pins, tied or 

 soldered together at their head ends, the points being in 

 opposite directions. This is mounted at its middle point 

 by means of sealing wax, to a long tube of glass. One of 

 these points when presented to the pin-point on the disk 

 will usually start the ball discharge, if it fails to appear. 

 It was found to be impossible to obtain these ball dis- 

 charges from the positive side of the machine. When the 

 teazer was used, these discharges would come from the 

 point on the teazer and would move towards the posi- 

 tive terminal. Plate I of this present paper shows such 

 discharges. At the top of the figure were placed two 

 disks armed with pins, which were connected to the + 

 and — terminals of the machine. Below were two sim- 

 ilar disks opposite to those above mentioned, mounted on 

 the same photographic plate, which was 10X12 inches in 

 size. 4 These disks were in metallic connection with two 

 large gas torches hung on insulated supports in the air 

 outside of the building. The torches were fed by means 

 of long rubber tubes, ending in short metal pipes to which 

 the line wires were soldered. Ball discharges came one 

 after the other from the negative terminal, some of which 

 went to the torch terminal opposite, some turning to- 

 wards the positive terminal of the machine. Ball dis- 

 charges also appeared from the torch opposite the posi- 

 tive terminal and went to that terminal. The plate was 

 exposed and developed in daylight, the developer being 



4 Separate plates for the + and — circuits permit them to be more 

 widely separated, and give better results. Smaller plates may then be 

 s < . 



