Signalling across space without wires / being a description of the work of Hertz & his successors

Chapter 51: APPENDIX VI.

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Engineering & Technology Science - Physics

About This Book

A technical lecture and extended essay presents Hertz's experimental demonstration of electromagnetic radiation and follows subsequent laboratory work and engineering attempts to detect and exploit those waves. It explains radiation, absorption, and syntony, reproduces key experiments with oscillators and detectors (including Branly filings tubes, the coherer, and early telephone receivers), and examines phenomena such as reflection, refraction, and polarization. Later sections survey adaptations for wireless telegraphy, report demonstrations by several investigators, and trace the historical and practical development of coherer-based signalling, with appendices summarizing related photoelectric research and practical remarks on apparatus and patents.

APPENDIX VI.

ELLIPTICALLY POLARISED
ELECTRIC RADIATION.

Since the delivery of my lecture to the Royal Institution, on June 1st, Herr Zehnder has published[41] a mode of getting elliptically and circularly polarised electric radiation. He takes a couple of plane polarising grids, such as are depicted in Fig. 21, page 37, and places them parallel to each other at a little distance apart with their wires crossed.

If the two grids are close together they will act like wire-gauze, reflecting any kind of polarised radiation equally; but if the warp and woof are an eighth-wave length apart, and the plane of the incident radiation is at 45° to the wires, the reflected radiation will be circularly polarised. A change in the circumstances will, of course, make it elliptical. Such a pair of grids acts, in fact, like a Babinet’s Compensator.