[LB011092], Letter from Thomas Alva Edison to Edward Hibberd Johnson, January 15th, 1882


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[LB011092], Letter from Thomas Alva Edison to Edward Hibberd Johnson, January 15th, 1882

Editor's Notes

Your letter 23rd December 1881.##As to the fact that the [za-engine] [enhance] the economy of our system I would not be quite so sure of this for the reason that if you take into consideration the interest and depreciation the Dynamo and its applicances and the life of the lamp and their cost you woulf find that that it would not turn out to be true. If you attempt to make it true by increasing the economy of the lamps you will get [left] by the lessened life of the same [---] You are quite right in stating that [--- ---] the main factors (in fact the principal factor) in the commercial introduction of our system in the high resistance lamp. The real factor is the greater number per horse power providing the life is always kept the same or is not diminished by the increased economy This reduces the investment in Dynamo steam engines & boilers in proportion to the increased number per horse power.##In the Painter Proof you sent me you say "of course it is a well known [---] that a given amount of heat acting upon two [boilers] one a large and one a smaller one will produce results in proportion to the ratio of their size." You should not have used the word heat but should use the energy instead##As to the words "out of the globe and leaving the carbon in a atmosphere of such exceeding [rarity as to preclude the radiation of any material degree of heat from the walls of the "globe" you must take out the word radiation and put in the following: "As to preclude the car--ing] by [--=mersion] of any material [defers] of heat" The reason for making this alteration is that when the globe is perfectly exhausted all the light and heat is radiated to the globe and through it. In fact in a perfect lamp all the light is radiant while if there be air in the globe heat is carried through the globe by conversion currents of the air##You speak of others obtaining a thin carbon. Where do you find a reference to other people using a thin carbon?##You say "this is done by sealing them in a vessel containing nitrogen and gases and electrically energizing them. You should say "sealing them in a vessel containing hydrocarbon##In connection with this building up process you might mention that this form of carbon thus deposited is amorphious in its structure and does not withstand the carrying action of the Electric Current in the vacuum as well as naturally arranged carbon.##You will find in a carbon patent (2492 of 81) a claim for copper wires soldered to the patina wires within the vacuum so as to save platinum. You will also find I think several patents on the method of carbonising the fibre##Your letter Dec 29th. I I think you will find upon making further enquiries about the price of the Siemens machine as compared to our machine that ours at the price you gave will in all cases be found cheaper than Siemens when you take into consideration the amount of horsepower applied to the amount of light on the same nunber of lamps of the same candle power. Siemens machines according to [Jeoph-sons] [text] when the value of his standard cell is connected a [ontzr] 83% machine scientific efficiency and with incandescent lamps I do not believe he will get more than 55 or 60% [ofs] the lamps I even doubt if he got this much. Their machine besides are not nearly as solid and substantial as ours. We can of course skim our machines down and make them cheaper. I think I could build the present machine or rather alter it so that it would only cost $350 but it would reduce the economy and increase the subsequent troubles of taking care of it. We cannot possibly lower our price because we only made $15 each on the first 100 machines the stock itself without any labor cost $[310]. By making the field magnets one third as long & by [lowering] a horsepower in the field magnets making a shallow commutator with only a few blocks and the Iron cores of thick plates - this would enormously reduce the price but it appears to me that I would sell the present Dynamo and not the inferior one even if I did not well as many as in the long run we shall come out ahead.##I do not believe you will have any trouble with your lamps; to be sure the lamps which you have are not so good as those turned out now but they certainly have over a 600 hour life. You must remember that if you put up 100 lamps and run them at sixteen candles for 6 hours there will be two or three go in the first night sometimes as many as four the next night two the next two or three nights after probably one and then they will run along for five or six days without one going. The weak lamps are all short out the first three or four nights. I will bet my life that if you keep these lamps at sixteen candles and keep a time record they will last over 600 hours average. Except possibly the "B" lamps which may possibly not go over 500 hours but I suggest that you order with new sockets 2000 of our new lamps and if you keep them at 1[6] candles and they last on an average of 800 hours I will agree to [-at] them. In running our old curves considerable number of lamps arced but of course they were at 48 candles thus showing a great improvement in this respect.##Note. Upton has just come in while I am writing this from my notes. He says that not one single lamp has arced this year.##About Motors. You can put half a dozen regular "Z" Dynamos machines & all "A" lamps anywhere on your main conductors and putting in ten or fifteen ohms resistance in the circuit with the Dynamo: place it [around] the conductor the same as a lamp then close the circuit and the Dynamo will start off and then you can keep plugging out the resistance until you have got it all off and the Dynamo will run 1500 or 1800 revolutions a minute and only absorb one half a horsepower so if you have six of these Z Dynamos used as motors only to run themselves you will use only about three horsepower but to make it more effective you should run a belt from one or two of them up to a pulley in Journals connected to the wall or on the floor This will give the idea of motion. You can also after the Dynamo has been started and is running and all the resistance is out [rig] up some [scarbling] so that persons can [buy] and stop the Dynamo but do not rig the [scandling] so powerful as to enable them to rducr the velocity below 600 or 800 revolutions and then you will only absorb 6 or 7 house power out of that one particular Dynamo.##My impression is that you can get the "Z" Dynamo field magnets and [brace] on boxes contracted for in England much cheaper than we can get them here on account of the low price of material if so we could send you the Switch Armature with shaft compl[ete]##We shall send you by next steamer a 15 "A" Light machine. The speed I think necessary to get the proper electro motive force up is 2000 revolutions per minute. It will work twenty five lights without materially heating but we call it a 15 Light machine. Make use of this as a motor and it will give about two hours power. As this machine will run 40 B lamps and can be made for probably $225 or there abouts you might compare this with the capacity of a Siemens Machine at [-90].##The Armington & Sims (owing to twice being in a state of [transition] from Lawrence to Providence) engines which you ordered have not come to hand The price of Engine complete for running one "Z" Dynamo very economically and two Dynamos pretty economically in $550 but the price list we sent you would would be quite sufficient when transmitting to you by an engineer. The engine required depends entirely on the Boiler pressure. If with 8 lbs a certain engine will only run two Dynamos with a certain economy you can increase the Boiler pressure so that it will run two Dynamos with the same economy as it will run one with a lower boiler pressure##Your letter 31st. Dec. I am sorry to say that in your argument with [Bidwell] you have made a mistake. You are generally right but in one of the details you are wrong. You state that one lamp of 125 ohms has one [ampere] of current passing through it. If you take one "A" Carbon there will be one Ampere passing through it and it will give say 16 candles. If you cut it in two parts you will have two B lamps and if these two parts are multiplied [arced] you will have two amperes passing through them. (i.e.) an empere through each hence we get 16 candles but have two amperes yet the energy per foot ([b-] arc the same). If we divide these two parts into [--] we will have 4 parts each giving 4 candles total 16 candles. But there will be four amperes passing. If say the A lamp is 100 ohms and you split it up with 100 parts and multiple arc all these parts between your plates there will be 100 amperes passing from plate to plate and the total candle power will be 16 candles but the total resistance will only be one one hundredth of one ohm and not one ohm as you say because each part being one ohm multiple arcing 100 carbons of one ohm each wuld reduce the resistance [---] of one ohm. Hence if we leave [out] the loss of heat from conduction to the plates and say the loss is no more for the 100 peices than for one piece in an "A" lamp. You would have 16 candles and get the same number per horsepower as if it was a continuous fibre. You see that if you have a Carbon that gives one ampere and sixteen candles you may subdivide it into a thousand pieces and each will have passing through it an ampere Take for instance the rise of 16 candle B lamps in place of [10] candle A lamps there is exactly the same economy and number per horsepower but one has a resistance of say 1000 ohms while the "B" 16 candle lamps have a resistance of 25 ohms but the radiating surface and the number of foot lbs of enery radiated is exactly the same. So you see if we had a one ohm conductor and 100 "A" lamps 16 candles the aggregate resistance of the lamps might be one ohm hence if 10 horse power was used it would be divided over 2 ohms - 5 horse power would be lost in the Conductor and 5 horse in the lamps. If we should place 100 16 candle B. lamps instead of A lamps the aggregate resistance would only be 25/100 of an ohm vs 1/4 of an ohm and as the conductor is one ohm there would be 8 horsepower lost iin the conductor and 2 in the lamps. Of course if five horsepower is required to bring the lamps up to proper candle power it will require the same horse power for the B 16 hence we must increase the horsepower to 25 horsepower of which 20 horsepower will be lost on the conductor and five in the lamps and so on ad infinitum but if we put four times the mass of copper in the conductor it would reduce its resistance to a quarter of an ohm and as the resistance of the 100 B 16 candle lamps is 1/4 of an ohm the loss of energy would be the same as in the first instance with the A lamps.##To sum up:##The amount of copper necessary to use in the Conductors is in direct proportion to the resistance of the lamp under line conditions. If I spend in copper $100000 for 20000 100 ohm lamps I will have to spend $200000 for 20,000 50 ohm lamps all giving the same candle power.##Roughly to light the City of London each additional ohm of resistance in the lamp will effect a saving of $57[142]##If Bidiwell took your ampere illustration in he is not well up on amperes##You were all right only you shuld have said each column on subdivision uses one ampere and not one ampere for the whole.##I can see from the printed matter regarding the lamp that you are finding out a great many things that you did not know when you left. The printed matter is astonishingly accurate considering what llittle you have had to do with the energy portions of the scheme and with the connections made I endorse it.##I want to call your atention to another little funny thing regarding the economy of our lamp (that is to say a high resistance carbon) i.e that their bodies which are good conductors of heat are also good conductors of electricity and vise versa. Now we have determined that the loss of energy by conduction down the clamps is 256 foot pounds or one eighth of the total energy that it takes per lamp and this loss increases just in proportion as the length of the carbon decreases in its resistance. The loss by conduction when a platinum loop is used is so great that it does not get to full incandescence for half an inch above the clamps - an eighth of an inch above the clamps it is not even visibly red so you see there is another gain in economy by using high resistance carbons.##I have handed your letter of 23rd of Dec on Telephone to Insull to go into it when he can get a few spare moments I am much obliged to you for the information contained therein and with what we already know it will doubtless make matters clear. Gouraud wrote me again in regard to Glasgow Commission to Moore Staddard and also about the sale of United Shares by which I lost $25000 but he simply reiterated his former statement so I replied that I had no wish to carry on an interminable correspondence and should therefore add nothing in what I had already said in former letters So that is how the matter stands. Telegraph me the moment Gouraud gets my remaining United Shares quoting current prices of same.##I think the contract submitted by Mr Fabbri is all right with the exception of the alteration cable Of course not getting a large amount down hurt me as well as the purchase in England but they of course cannot understand how the extra payment of money to me can lend to their benefit although it certainly would ten times over. I suppose however that in the long run it will be better for us to have taken our money as it must add to the value of our shares.##It is not much use to say anything here about your big machine. We have got the brush business down fine excessively convenient and you will have no trouble from this as the current can be taken off a great deal stronger than the engine can run. Our main trouble is the Poreter Engine. After we got disgusted with it we brought Porter over and he became disgustedwith it and now he is rebuilding one of the Engines, and promises to bring it here by Tuesday, and says it will run silent and give no trouble and Mr Fabbri thinks we had better wait for this. We will send you a full letter regarding the workings of the machine when we ship it.




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