[LM112159], Letter from Arthur Edwin Kennelly to Edison Lamp Co, Francis Robbins Upton, November 2nd, 1889


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The Siemens Alternating Dynamo sent to you yesterday gives 200 mean alternating voltage when running at 1500 revolutions per minute with about 5 amperes in the field circuit. We hope you will return it to the laboratory when your purposes with it are accomplished. ## Mr. Edison's municipal automatic cut out consists of a pair of metal spring strips each connected with one leading wire of the lamp, and separated by the insertion of a lamina of silver sulphide about 0.01" thick. The sample strips tried were about 1/2 x 1/4". The resistance of this cut out is very high normally but falls very rapidly on the application of heat. The sulphide was prepared by the action of [some silver compound] and the precipitate mixed in a crucible under hydrogen then rolled into strips. We tried two or three lamps protected in this way for several days and they showed no appreciable leakage, but a pressure of 100 volts brought to bear upon the strip produced a current through it whose heat instantly reduced the sulphide to metallic silver, so rapidly in fact that the decomposition of the wire leading to the protected lamp only produced a momentary flicker in [illeg] in circuit. The only danger to be feared is apparently the heat in the neck of the lamp where the cutout would presumably be inserted. We did not try [any?] strips in the neck but Mr. Edison did not think the damage too great. ## I have no doubt that the laboratory can furnish the rolled silver sulphide from its chemical department if [application] be made. We have none on hand.








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[LM112159], Letter from Arthur Edwin Kennelly to Edison Lamp Co, Francis Robbins Upton, November 2nd, 1889

Microfilm ID



Thomas A. Edison Papers, School of Arts and Sciences, Rutgers University