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 'hammer-and-anvil' form is, of course, the portion which is sensitive to sound.

The microphone is a discovery as well as an invention, and the true explanation of its action is as yet merely an hypothesis. It is supposed that the vibrations put the carbons in a tremor and cause them to approach more or less nearly, thus closing or opening the breach between them, which is, as it were, the floodgate of the current.

The applications of the microphone were soon of great importance. Dr. B. W. Richardson succeeded in fitting it for auscultation of the heart and lungs; while Sir Henry Thompson has effectively used it in those surgical operations, such as probing wounds for bullets or fragments of bone, in which the surgeon has hitherto relied entirely on his delicacy of touch for detecting the jar of the probe on the foreign body. There can be no doubt that in the science of physiology, in the art of surgery, and in many other walks of life, the microphone has proved a valuable aid.

Professor Hughes communicated his results to the Royal Society in the early part of 1878, and generously gave the microphone to the world. For his own sake it would perhaps have been better had he patented and thus protected it, for Mr. Edison, recognising it as a rival to his carbon-transmitter, then a valuable property, claimed it as an infringement of his patents and charged him with plagiarism. A spirited controversy arose, and several bitter lawsuits were the consequence, in none of which, however, Professor Hughes took part, as they were only commercial trials. It was clearly shown that Clerac, and not Edison, had been the first to utilise the variable resistance of powdered carbon or plumbage under pressure, a property on which the Edison transmitter was founded, and that Hughes had discovered a much