[Fig. 62.—Portable pack set.]

[Fig. 63.—Complete receiving set.]

[Fig. 64.—Showing the construction of a watch case telephone receiver.]

[Fig. 65.—Pickard adjustable telephone receivers.]

[Fig. 66.—Illustrating the valve action of a rectifying detector.]

[Fig. 67.—A new type of silicon detector.]

[Fig. 68.—Diagram drawing analogy between rectifying action of a detector and pump.]

[Fig. 69.—Pyron detector.]

[Fig. 70.—Perikon detector.]

[Fig. 71.—Silicon detector.]