[D8939ABN], Letter from Francis Jehl to Francis Robbins Upton, March 21st, 1889


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[D8939ABN], Letter from Francis Jehl to Francis Robbins Upton, March 21st, 1889

Editor's Notes

This the copy of Jehl's letter to Upton that appears Upton to TAE, D8939ABM 890507: The following is an extract from a letter which I received from Francis Jehl, dated Brunn, March 21st.####"I have seen the lamps I wrote to you about. It is not exactly as I then thought. It is in no way similar to the present lamp that is like ours.####"This figure will show you how the lamp is. It consists of two electros or plates of platinum or carbon, A.B. as shown (not in connection but simply facing each other) asn when a current of a certain description is connected at the ends C & D, there is a small blue arc== in the beginning and then all at once these paltes become incandescent and give out light. The Dr. inteds only to use carbons electros as with platinum ones the heating point is too low and they melt. I have seen some lamps having platinum electros and with about 3000 volts they glowed very brightly and the distance between them was abou 8 m/m. There is a vacuum in the lamp but not but not very high. If the vacuum is high the spark will not jump, and if very low there will be a sparking, but the plates or electros will not glow. He is now working on carbons plates and intends to use gases in the lamp rarefy to the extent required. In the lamps of carbon plates the electros are very near to each other perhaps a about 1 m/m apart. I have seen some lamps and they gave a pretty good light. Now the other part of his system has also some good points as it saves copper in the conductors. He does not send 3000 volts from the station to the place of consumption as one might at first suppose, but his system is something as follows####[over]####[Note: There is a diagram on the left hand side of the page]#####is a continuous current machine, one having very little or no self induction and giving any 400 volts or anything we please according as we wish to save in the colnductors. The current passes through the lines 1 & 2 into a disjunctor B. (an apparatus for reversing the direection of the current). This current charges a condenser C which discharges through a sort of induction coil D, the secondary of which is connected with the extremities of the glow lamp E.####One is apt to think that it is not possible to change the direction of a current in the dynamo machine without causing a cross or interruption and sparking. This however is not so in this case, because when the current charges the condensers, and the condensers are charged, there is no current flowing in the line at that mokment and because the tension of the condensers is the same as that of the dynamo, but opposite, thus equalizing. At this moment the poles are changed at the disjunctor. He used a very high rate of discharge or rather revversal very much more than that used in transformators. He ccarries the low volts up to the lamp and only at the lamp the high volts are generated as he intends each lamp or group of lamps to have such an induction coil "D which in itself is very small, being about 8 centimeters by 4 large. He has also shown me this same system of distribution working our lamps. Of ccourse in this case the induction coil "D" was wound differently. I have thus given you the outlines of this system which will help you to form an idea of it. You have asked me if you can tell it to Mr. Edison, why certainly, I consider myself always yet belonging to him, as today I am in the company yet to which he sent me. I heard Mr. Edison had an accident, but was ery happy to hear afterwards that it was not serious."####Yours very truly,####Francis R. Upton####[name mentions: Francis R. Upton, Thos Edison, Francis Jehl]





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