CHAPTER VIII.
CHARGING AND DISCHARGING CONDUCTORS.
138. The Electrophorus. While the ebonite sheet alone, or a good hard-rubber comb, may be used for many experiments in frictional electricity, the sparks produced are small, and the ebonite has to be electrified as often as it is discharged. To obtain real good sparks, and to avoid this continual rubbing, the student should be provided with an e-lec-troph'-o-rus. This is, really, a simple, cheap, and efficient frictional electric machine. An electrophorus consists of 2 insulators and 1 conductor—that is, of 3 parts: (1) insulating handle, (2) cover, and (3) a plate or base of insulating material.
139. Our Electrophorus is shown in [Fig. 34]. For the insulating handle use the ebonite rod, E R (No. 28); for the plate, use the ebonite sheet, E S (No. 26). The electrophorus cover, E C (No. 42), furnished, is a tin box with a fancy top. A hole has been punched in the center of its top, and into the hole has been riveted a short tube, so that the handle, E R, can be firmly held. The hole has been made a little larger than E R for convenience. To make E R fit tightly in the hole, so that you can lift E C, wrap a small piece of paper around the end of E R before pushing it into the hole. You can easily find out how much paper to use to make a good fit. With a knife cut away all loose points of paper that stick out of the hole around E R; this is important. The top and bottom of E C should be pressed firmly together.
First learn how to use the electrophorus. With the large amount of electrification produced we can then find out how it works.
EXPERIMENT 68. To learn how to use the electrophorus.
Apparatus. Shown in Figs. 34, 35. Do not fail to read [§ 139].