Signalling through space without wires : being a description of the work of Hertz & his successors . as when it waspresent, in accordance with the theory of Poisson. Add thelens and the effect is greater. With a diffraction grating ofcopper strips 2in. broad and 2in. apart, I have not yetsucceeded in getting good results. It is difficult to get sharp 40 SIGNALLING WITHOUT WIRES. nodes and interference effects with these sensitive detectors ina room. I expect to do better when I can try out of doors,away from so many reflecting surfaces ; indoors it is liketrying delicate optical experiments in
Signalling through space without wires : being a description of the work of Hertz & his successors . as when it waspresent, in accordance with the theory of Poisson. Add thelens and the effect is greater. With a diffraction grating ofcopper strips 2in. broad and 2in. apart, I have not yetsucceeded in getting good results. It is difficult to get sharp 40 SIGNALLING WITHOUT WIRES. nodes and interference effects with these sensitive detectors ina room. I expect to do better when I can try out of doors,away from so many reflecting surfaces ; indoors it is liketrying delicate optical experiments in a small whitewashedchamber well supplied with looking-glasses; nor have I eversucceeded in getting clear concentration with this zone-platehaving Newtons rings fixed to it in tinfoil. The coherer, atany rate in a room, does not seem well adapted to interferenceexperiments; it is probably too sensitive, and responds evenat the nodes, unless they are made more perfect than is easilypracticable. But really there is nothing of much interestnow in diffraction effects, except the demonstration of the. Fig. 22.—Zone-plate of Tinfoil on Glass. Every circular strip is of area equal to central space. waves and the measure of their length. There was immenseinterest in Hertzs time, because then the wave characterof the radiation had to be proved; but every possible kind ofwave must give interference and diffraction effects, and theirtheory is, so to say, worked out. More interest attaches topolarisation, double refraction, and dispersion experiments. Polarising and Analysing experiments are easy enough. Eadiation froma sphere, or cylinder, or dumb-bell is already strongly WORK OF HERTZ LECTURE. 41 polarised, and the tube acts as a partial analyser, respondingmuch more vigorously when its length is parallel to the lineof sparks than when they are crossed; but a convenient extrapolariser is a grid of wires something like what was used byHertz, only on a much smaller sca
Size: 1579px × 1582px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1900, bookidsi, booksubjectelectricity
