[LB011142], Letter from Thomas Alva Edison to Edward Hibberd Johnson, January 23rd, 1882
Your letter of 6th inst came duly to hand.#3Regarding the text by Sir Wm Thomson I do not think silk winding is so good as wire winding. On the big Dynamo we use 1/16 in pianofork wire for in[winding], the centrifugal force being so very great There is no trouble with the Dynamos now as we bore the hole in the field out very much larger. The trouble in all Batchelors machines was that the fields were too small and the momentumof the parts swelled the armatures and caused them to catch. Even the machines you have could have a space of 1/8 of an inch more than they now have & still the field magnet would be sufficiently powerful to bring them up to the required volts. To give me proper data to ascertain about the Siemens machine please give me the internal resistance of the field magnets the number of volts across the terminals of the machine when the full load of lamps are on. I should also like to have the number of volts across the terminals when the external resistance is fifteen times greater than that of the internal also ten times and five times. I would also like to know the diameter of the armature and its length and the velocity at which the test are taken also the amount of resistance in the field magnet and the variation it makes in the number of volts when the machine is worked ten to one.##Do you know that I have the impression that we were the first in England to multiple arc the field across the line containing a resistance for regulating the strength of the field and I am quite sure that we were the first to regulate the field of force magnets by pulling in the field of force [circuit] an adjustable resistance. Please look through the patent for this point. I think before [loing] the [boot] will be on the other foot and a good many of these [Dynamos] will e infringing this [-parent] Siemens for instance.##You spoke about the greater economy of our machine being an important advantage over the Siemens machine when the prices are mentioned But as there not another element concerned which is that our machine will run more lights. Upton is now making your hundred candle power lamps He is also going to make a lot of 150 candle power lamps of pretty good economy and 600 hours life for use against the arc men here. For instance we get into a factory where they have already brought a arc machine which gives a dozen or fifteen arc lamps and which is the property of the concern where it runs we take out the arc lamps and substitute a 150 candle Incandescent Lamp requiring the same horse power as the arc lamp the whole of them being worked in series so that no changes are made the whole being perfectly [stecded] and giving a large bolt of five and no light being lost by a ground glass globe Our idea is that they will much prefer to run these lamps than the arc lamps. Such being the case we will get the future [rate] of these lamps which if they last 600 hours are far more commercial than the arc lights for the reason that it costs a cent and a half an hour for the Carbon which will be nine dollars for 600 hours wherean we can afford to sell these lamps for three or four dollars. The 8 1/2 p. E. h. p. lamps giving 6 p. I. h. p. Armington and Sims small engine you can guarantee with perfect safety [Price] average life will be 600 hours providing they are run at the normal candle power of Sixteen candles. In fact these lamps will last twice as long but it is best to say that they will last 600 hours because our statement will more than come [true] and it will establish a confidence in the same ratio as a loss of confidence begot by the proverbial and persistant liars who infringe our rights. we are going to test the Disc Dynamo in a few days and if everything is satisfactory will ship it at once to you for Sir William Thomsons test##Our last test of the large Dynamo showed about 6 3/4 lamps sixteen candles each per [i. h. p. undoubtedly it gives seven p. i. h. p. as when we first started we only got about five p. i. h. p. but figuring out cru[us] in the Indicator and other places have gradually brought the economy up It is extremely difficult to indicate these powerful high speed engines and get anything like a proper & true indication as there are so many sources of [cruo-] when we first started there was a loss of 45 h. p. now there was no place so heated now was the heat of all the aggregate heat of all the parts sufficient to account for more than a loss of ten h. p. hence we knew the cross must be in the Indicator and by gradually finding out the cross we have reached higher economy. we had decided after running the Poreter Engine on and off for a week and the last three nights all night long to accept Mr Porters offer of a new Engine that is to say the same kind of an engine thoroughly over hauled and everything put on alinement. After I determined to take the Engine off I thought I would try an experiment with the Dynamo. So we [brought] the boiler pressue up to 158 lbs put on  lights and brought the volts up to 117 the lamps being 100 volt lamps and calculated that we had the equivalent of 1650 lights on the machine There was no trouble at all with the Dynamo nor was there with the commutator but after running three minutes the cupplying broke from pure incapacity to stand such an enormous strain. The engine must have been developing between 220 and 230 h. p. This cuppling that broke was made of cast iron. we shall put in steel cupplings with the new engine. You will be highly pleased with the new brushes and commuttor arrangement we spent $1500 in experimenting on brushes as we found that the sparking increased as the internal resistance of the machine decreased. You will have no trouble on this score. I will write full instructions about these matters when the machine is ready for shipment.##I understand from Barker that his test of Swan Lane [Faxes] lamps at Paris Exposition that they measured only 27 ohms hot when giving 16 candles Maxims averaged 52 and ours 148. From this I imagine that both Swan and Lane [Pos] [check] to even up their [botch] work by the deposit of carbon from the hydrocarbon like maxim. If this is true Swan does not seem to succeed very well at the Savoy Theatre. These fellows will find out the longer they keep at it how extremely difficult it is to make Electric Lamps by the thousand with long life and even candlepower.##Down at the Lamp Factory we are gradually narrowing down the variation in the volts. Our output in December all came within seven volts of each other and I believe that we shall be able in the [w--red] of six months be able to make all our lamps of the same volts and candle power. Upton has sent you a [life] test of twenty seven lamps put up at 16 candles, after I had got the Factory on its feet again making [first] glass lamps. You will see that those have remarkable life and we calculate that they will last about twelve or thirteen hundred hours on an average. I have not succeeded very well with the Spiral High Resistance lamp. There is a difficulty in making the lamps 250 [ohms] 11 H. p. E. h. p. but they have a very brief life and it will take some time to bring the life up to the proper standard. This is perhaps a good thing as the [extreme] difficulty is one of our best precautions. The present lamp is Childs play as compared with the lamp I am now working on.##It may possibly interest you to know that the maxim Light has been taken out of the Jewellers Store in Eighth Avenue out of the Cafe of the Hoffman Hoffman House the Equitable Bldg, Fisk & Hatch, [Hotels] & Foote & abandoned at Cincinnati leaving them only Caswell & Hazards Drug Store and the Penn. R. R. Ferry Boat. It may also interest you to know that we received a leter from the Penn. R. R. People asking us for an estimate to light up all the Ferry Boatsmaking the specification almost identical with the maxim Plant now in one of the Boats but saying nothing about the life of the lamps nor the power which conclusively proves that ths asking us to bid is merely a blind to cover up a scheme as we are informed that Thompson is interested in the maxim Light. We are going to bid notwithstanding giving them the regular prices and under their little scheme [nugatory] by writing them a letter calling attention to the fact that the life of the lamps and the economy of the same have been left out of the Specifications.##We enclose you list of Isolated Plant installed to date. I also enclose you several copies of the last rules adopted by the Board of Underwriters which rules were suggested by us and adopted by them after consultation with all the Light Companies and arguments before the National Board of Free Underwriters. We received the copies of the morning advertiser containing your article which is first class in every respect and has been very favorable commented on by Mr Fabbri Lowrey and others.##I do not know whether I shall see D'oyle Carle but Oscar Wilde to whom D'oyle Carte is agent has expressed a desire to call on me. So perhaps I may also see the caller named gentleman##We have sent you some copies of Du moncels Article & Howells Paper from Van Nostrands magazine by Wells Fargo Express. Van Nostrand is now printing a small Hand Book forming one of [their] Science Series containing Du Moncels Article Preeces Lecture & Howells Test with an article by Siemens besides Please say how many of these you want. Howells Test was made with the Bar & Disc machine which Batchelor has Thompson will be pleased with this. I will with the aid of Insull try and get up a letter on Preece & enclose it to you for delivery##I cabled you that in the new Large Volumes of my Telephone Interferences with which you are familiar there is an exhibit [7-12-1] dated July and the other August relating to the Phonograph sowing that I had the thing in my mind when I filed the Provisional Specification on the patent you are now litigating. I hope you have the Volume. Batchelor had it at the Exposition so I will not send you one. I think you will also find in the back part of that Book on in the smaller volume all your lectures and the necessary material you desire on that subject. The idea came of [source] from that morse operator with the spiral on the Disc for recording morse characters and reproducing the same from the identations which were made long previous to the filing of the English Specification##Could you not hire a boy and station him at some point were he could see the nighly burning of Swans lamps to ascertain their life.
[LB011142], Letter from Thomas Alva Edison to Edward Hibberd Johnson, January 23rd, 1882
Thomas A. Edison Papers, School of Arts and Sciences, Rutgers University
January 23, 1882