This is a chart of the electromagnetic spectrum, published by the W.M. Welch Scientific Company in 1944, and posted online about three years ago. It covers electromagnetic radiation from simple diffraction to cosmic rays, and shows the frequency allocations and their historic use across the spectrum. (full resolution image is here)
When Nikola Tesla established his first laboratory on Grand St. in New York in the mid 1880s, he began to experiment with high frequency electrical phenomena, initially to reproduce the frequencies of sunlight. He invented for this purpose a ‘Tesla Coil’, a high frequency transformer that takes the 60-cycle frequency of alternating current electricity, steps it up to hundreds of thousands of cycles per second, and generates extremely high voltages. With these experiments he made a radical departure from conventional physics. Tesla had discovered a different form of energy which he called ‘compressed voltage’ or the ‘aether’.
Tesla presented the results of his initial experiments with his new invention in a lecture / demonstration at Columbia College in 1891, stating that the energy produced by his coil was not electromagnetic.
Tesla said: ‘When an induction coil is used, there is no doubt the (Geissler) tubes are excited by electrostatic induction, and that electromagnetic induction has little, if anything, to do with the phenomena. For instance, if a tube be taken in one hand, the observer being near the coil, it is brilliantly lighted and remains so no matter in what position it is held relatively to the observer’s body. Were the action electromagnetic, the tube could not be lighted when the observer’s body is interposed between it and the coil, or at least its luminosity should be considerably diminished.’ …there is a possibility of obtaining not only in the form of light, but motive power, and energy of any other form, in some more direct way from the medium.
The time will be when this will be accomplished, and the time may come when one may utter such words before an enlightened audience without being considered a visionary.’
Read the full lecture here and a review of it from The New York Timeshere.