[Fig. 82.—Interior of rotary variable condenser, showing construction.]

[Fig. 83.—Dr. Seibt's rotary variable condenser.]

[Fig. 84.—Sliding plate variable condenser.]

[Fig. 85.—Diagram showing arrangement of rotary variable condenser in receiving circuit.]

[Fig. 86.—Chain and ball arranged to illustrate the effect of tuning.]

[Fig. 87.—Loose coupled helix.]

[Fig. 88.—Hot-wire ammeter.]

[Fig. 89.—The principle of the hot-wire ammeter.]

[Fig. 90.—Diagram showing loose coupled helix in circuit.]

[Fig. 91.—Loose coupled tuning coil.]