[LM111117], Letter from Arthur Edwin Kennelly to Non Magnetic Watch Company of America, A C Smith, September 10th, 1888
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Title
[LM111117], Letter from Arthur Edwin Kennelly to Non Magnetic Watch Company of America, A C Smith, September 10th, 1888
Editor's Notes
"I beg to forward herewith on Mr Edison's behalf my report to him upon the behavior of the watches tested for you. In making out this report I have endeavored to represent all the facts truthfully and impartially. Mr Edison desires me to say that if you publish this report it must be published in extenso or at least that no part will be omitted without his sanction. For example the appendix relating to the gain of the watches in a powerful field, and other points not practically important? do not doubt he would consent to you omitting if you desired it. The -ast connected with the gain of these watches during their subjection to powerful magnetic is very interesting from a scientific point of view and quite in accordance I believe with the recognized theory of electromagnetism. I should like to write a pape to one of the electrical journals on the subject dealing with the matter ---- on its scientific aspect, and would be glad to know if you will allow me to do this. If so I would submit the Paper for your journal after Mr Edison had sanctioned it and before offering it to the journal.####Trusting that the report willmeet with your satsifaction.####I am Sir####Yours very faithfully####A.E Kennelly####[page 43]####[chart]####The following tables give the record for each watch during that time. Column I gives the date of 2- and Column II the clock time of cash comparison. Column III gives the ---- of the watch by the clock at that time. The next column No IV gives the difference of ---- or mean rate from day to day and when the times of observation have been not separated by the due term of 24 ---- the correction to ---- daily rate follows in Column V. The --- temperature and position of the watch for each intervening 24 hours recurs in columns VI and VII####[page 44]####(a) Magnetic Tests.####The magnetic tests of the watches commenced on the 18th August immediately after the temperature tests, and acriti---- till the 24th August, a few special magnetic experiments, however, were made up to the 30th August. Desiring this interval the watches were subjected to magnetic stresses of successively increasing magnitude and from ---- carefully noted between cash experiment The -- [Starn?] watches numbered on the above list 18, the 15, 16 & 17 being unprotected and magnetable were left out of this trial. The watches magnetically tested were this####Nos 6 and 9 unprotected and with ordinary steel hairspring-####Nos 7 and 8 watch with steel hair springs failed with the Giles Antimagnetic shield protection -####Nos 4, 5 and 18 Waltham watches with hairspring of non magneteable metal####No 10 A Pat--- Philippe watch ---- hair spring of non magneteable metal (----------)####No 1, 2, 3, and 12 "Non Magnetic" Watch 6: [crossed out] watches with hair springs of palladium alloy.####The first experiments were made in the Dynamo Room of the laboratory. With this object in view the above watches were transported there on the 11th morning of the 11th August and allowed to run there for two days out of ---- of all dangerous reach of the dynamos so as to obtain these rate at the mean temperature of the room. Those rates appear in the appended of the watches for those date and do not appear to differ appreciably from the####[page 45]####for the first morning of the 13th August, I --- watches were rated as usual at 8:15 and tested with a ------ compass for magnetism No 10 -- were the only watch that gave distinct indication of free magnetism. They were then -aid dial up in close proximity on two shelves of a small wooden case and the case was placed near a large Edison Dynamo [crossed out] at such a position as any person coming forward as a stranger to examine the machine might naturally take up. The distance between the watches and the nearer pole of the dynamo was 130 --- or water 4 feet 4 inches. The strength of the magnetic field at this position when the watches were removed was measured and found to be approximately 83 units (C.G.S. units) This field is probably the most that a dynamo visitor would be likely to expose his watch to except under special circumstances. The watches were exposed to this field from 9.18 to 9.11, they were then tested for permanent magnetism and were all found to be very slightly magnetic. They then were allowed to run until the follow morning in the dynamo room, but before out of effective magnetic range. The records shore--- appreciable changed in the rated of either the ----- except for the usual rating, the watches were left undisturbed until the morning of the 15th when the test of the 13th was repeated with somewhat more severity by placing the case containing the watches close to one pole p-se of the dynamo on the --- outer side that is to say on the opposite side to the armature. The mean strength of the magnetic field at this position are found to be 200 units. After remaining some few minutes in this field they were removed and found to -- all poss--- decidd magnetic qualities The unprotected watch No 6####[page 46]####stopped, and the other unprotected watch No 9 showd a mean losing rate of 1660 seconds for the --st 24 hours recovering to great extent its removal rate in 48 hours. The effect of this experiment is also evident in the case of Waltham watch no 5. which retards its rate 13 seconds in the rest no viable change is their time, kept out of range ---- the dynamo room####The next test took place on the morning of the 17th August, when the watches were placed dial up between the poles of the same large Edison dynamo for ten minutes. The dynamo was running, and the watches lay on the brass wire grating above the rotating armature in the groove between the pole pieces. The mean [magnetic?] field in this position from several measurements was found to be 590 units. By taking the rate of the watches before and after this test it was found that Nos. 3,5,6,7,8, and 9 and 10, had stopped, [crossed out] during the experiments, and the unprotected no 9 was too heavily magnetized to run afterwards. It was therefore set aside.####The rates for the next day with the watches out of magnetic [range?] in the engines room show by the appended records in slight ac----tion in Walthams 4 and 5, a ---- retardation of 2700 seconds in unprotected no 6, an acc---vation of 300 in shielded no 7, a retardation of 400 in shielded no -, and no appreciable alterations in any of the others.####The next experiment was made on the morning of the 20th August when the watches were placed dial up between the h----- poles of a powerful electromagnet for five minutes. The mean strength of the field ---- at the position occupied by the watches was found by measurements before and after the experiment to be 1260 units, every watch stopped on being placed####[page 47]####hortizontally in this field, but all continued running on removal. After this trial the watches were no longer kept in the dynamo room but in the vicinity of the astronomical clock as before the 11th August. The records for the next 24 hours show####a retardation of 84 secs in Waltham No 4####a retardation of 9 - - No 5#####a retardation of 2470 - - unprotected no 6####a retardation of 656 - - shielded no 7####an acceleration of 960 - - shielded no 8####and no appreciable change in the others####No 1 2 9 10 12 and 18.####The next experiment was made on the morning of the 22nd August when the watches were set penda[nt up find one m----?] between the [triangle?] poles of the last mentioned electromagnet. The field in the absence of the watches was -------- found to be 290 units.####Watches 1, 2, 12 and 18 ran uninterruptedly through this test, ---- nos 3 4 5 - and 8 stopped momentarily on entering the field ----, no 7 stopped during the whole minutes while no 6 stopped and was too heavily magnetized to run afterwards. It was ---- set aside.####The records for the following 24 hours show####an acceleration of 17 secs in Wlatham no 4####an acceleration of 207 - - shielded no 7####a retardation of 1350 - - shielded no 8####and no appreciable charges in the rates of 1, 2, -, 5, 10, 12, and 18.####The last general comparison test was made on the ----ing of the 24th August when the watches were placed pendant up between the [horizontal?] pole of the same electromagnet. The poles in this case however were conical, with their points opposite each other. The magnetic axis between those was kept for uniformity ------ with the axis of the second hands of the watches.####[page 48]####The magnetic field between these two pointed poles of the magnetic axis was found to average in the absence of te watches 2900 units. All the watches stopped on entering the field except No 1 2 and 15. All continued runnning after withdrawal from the field.#####The records for the next 24 hours show a retardation of 15 secs in Waltham No 4####- - - 58 - - - - 5####an acceleration - 192 - - shielded - 7####- - -355 - - - - 8####and no appreciable changes in the rates of Nos 1 2 3 10 12 and 18.####This last experiment brought into operation the most powerful magnetic field that was at command, 3950 units across 2 centimeters of an space. It should be mentioned that the numbers given to the field strength mentioned above ---- although correct say within 5% for the magnetic stress in the air at the positions subsequently occupied by the watches will always be less than the actual field in and round the watches when these latter was placed in those positions, owing to the intensification and concentration of the magnetism by the ---- steel ------- screws and shields of the watches. This remark [applies?] more particularly to the experiment of and after the 17th August. As it could have been well nigh impossible to measure the field magnetic [steel?] in the watches when actually in the field, the above method of comparing the field inten---- has been rendered necessary####In the interim between these magnetic tests the watches were always left dial up.####The rating as the records show was always ---- ---- before and after a magnetic test to that any error ----- in the time of a watch produced by it stopping temporarily in the field, might not to ----- enter its next days rate.####Between the 20th and 30th August a series of experiments was made with the [Pailard?] Non Magnetic watches for the purpose of ascertaining whether they tended to gain or lose while running continuously in a magentic field. As the question is merely of scientific interest and has little practical value these experiments are described in a separate appendix.####The comparative behaviours of the watches may be briefly shown by the following table.####[chart]####[page 49]####Hair spring -----and temper test In these tests the d---ations of different hair springs produced after distension owing to imperfect elasticity were compared both at ordinary temperatures and after ---ting to redness.####The trials were made in our business at in Edison Laboratory by Ms Ward on the 17th August and by Mr Hubber on the 5th September 6th of the Non Magnetic Watch 6-####The springs experimented with on these occasions were as follows####[chart]####These springs were all taken from packets marked with the name of the maker, ----- in the case of No 10 The Waltham spring which not being it is said separately purchaseable was taken from Watch no 5.####The tests made on the 17th August were as follows One specimen of each of numbers 1, 3, 4, 5, and 8 was placed on the end of an iron spatula which was then heated over the flame of a pirit lamp. By this means all the springs were heated to redness. After allowing them to cool, they were then examined for deformation both in plane and in soil with following results####[page 50]####[chart]####These springs were now tested for elasticity by distension. The ends of each were gripped with ----- and drawn steadily apart to a distance of 16 cm (6 1/4 "). On allowing the spring to return to its manual position the plane was usually found to suffer. The distance between the planes of the outer and inner turns is given as follows.####[chart]####[page 51]####The next test was for deformation under sudden heating. One spring was heated on a copper ship to bright redness by means of a ------ in two or three seconds####[chart]####These trials were in substance repeated on the 5th September. The first test on that date was the distension without heat. The observations were as follows:--(after 15--- at 6 " slut-----)####[chart]####The next test was a compassion of the effect of sudden heaating the springs. An iron spatula was heated to redness and spring was ----####[page 52]####to fall upon it, both then cooling down and ---- effect on the spring was observed with the following results.####[chart]####These springs were then tested for distension loss of temper through heat by distending them 15 cms 16" and observing the distortion produced. The results were as follows:--####[chart]####[page 53]####To Conclusions [one line too faded to read] The [rest of the line too faded to read]from the above records and distention ---####1st That with regard to adjustment for temperature and position the [Paulhard?] Non Magnetic Co watch -- 1 2 and 3 purchased in the open market compare favourably with other standard watches of good adjustment, which no 12 lent by Mr St--- [behavior?] particularly well in this respect.####3rd That the temper and [cincteresly?] of the Paillard palladium alloy - hair springs experimented on as described above. Have been second only to that of the best [Dufors?] hair spring.####3rd That the elasticity of the Waltham non magnetic hair spring takesfrom watch no 5 is even allowing for its shorter length ----- more imperfect in elasticity than any of the specimens tried except the ordinary swiss springs.####4th That although the Paillard watches have sometimes stopped ------- on being submitted to normal magnetic field of 1260 or more units that none of the four experimented on have shown any visible alteration of rate after removal from the fields although they have been submitted to the most powerful magnetic st--- at our command.####5th That the Waltham non-magnetic watch no 18 lent by Mr St[orr?] has manifested an immunity from magnetic influence under all magnetic stresses equal to that of the Paillard watches but that the two Waltham non-magnetic watches --- ------ purchased in the open market have shown distinct alterations of rate under magnetic influence, although their hair springs are of non magnetic metal.####6th That the Patch-Philippe watch with non magnetic hair-spring has also shown an immunity to magnetic influence as complete as the Paillard watches and Waltham no.18.####[page 54]####7th That the Giles antimagnetic shield has to a certain extent protected the watches to which it was attached (nos 7 and 8) form magnetic injury. That is to say it has apparently completely shielded them from a magnetic stress which injured the unprotected watches on the 15th August, and it apparently mitigated the effects of the more intense magnetic field on subsequent occasions so that these watches although suffering heavily in their [ruts?], continuous to ----ing to the end of the test whereas the unprotected watches were quite disabled. It therefore fair to say thata stub hair spring which protected by one of these shields might be worn for months by a person engaged in dynamos or electromagnetic work without even entering a magnetic field of sufficient strength to affect its time keeping qualities, but, that the possibility of entering a magnetic field of the necessary intensity to [produce injury?] would always exist and the chance would sometimes occur. Whether the injury to the rate of a shielded watch would be under those circumstance arrangement or temporary, we are not in a position to say except that the seconds show in each case a tendency to return towards the original rate. It seems [however?] that a watch whose ---- ----- [ores?] magnetized and which has taken up a certain alteration of rate in consequence of its magnetic condition is more susceptible to such alteration under magnetic influence than in its previous magnetic condition. This would probably be the case with a once magnetized shielded watch in a lesser degree under the madifying return of the shield.####[page 55]####8th That the exper
ments made with the -----sion watch soon made to envelop the watch, seem to show a decidedly lesser degree of protection then the Giles antimagnetic shield, and consequently would fail to preserve a watch except in comparatively weak magnetic field.####9th That a Paillard Non Magnetic Watch or p------ any watch whose hair spring is of non magneteable metal tends to ------- on being exposed to a magnetic field except or when the direction of the field####his is the plane of the hairspring (2) when the hair spring shares to find no metallic communication between its clamp and through the balance wheel and framework.####The ------ however may be apparently disguised diminished or were d----ed by the --- greater friction brought to bear on the magneteable s--- --- and working parts of the watch during the [perates?] of the magnetic stress.####I am Sir,####Yours faithfully####A.E. Kennelly.####[page 56]####8th That the experiments made with the -------- watch soon made to envelop the watch, seem to show a decidedly been degree of pretection then the Giles antimagnetic shield, and consequently would fail to preserve a watch except in comp----- f--- weak magnetic field.####9th That a Paillard Non Magnetic Watch or preserving any watch whose hair spring is of non magneteable metal tends to ----- on being exposed to a magnetic field except or when the direction of the field is in the plane of the hair spring (2) when the hair spring [stances?] to find no metallic communication between its clamps and through the balance wheel and framework.####The [peaimates?] however may apparently be disguised diminished or even [decreased?] by the [first?] greater friction brought to bear on the magneteable steel --- and working parts of the watch during the p----- of the magnetic stress.####I am Sir####Yours faithfully####A.E. Kennelly.####[page 57]####Aps--ai-####Comments made to determine the effect of a magnetic field on the rate of a watch whose brass spring is of non magenteable metal.####The watches experimented on were the Paillard no 1, 2, and 12. The ---- rates of their being steady and viable.####The first trial took place on the morning of the 25th August with the watch not placed pendant up with its balance wheel axis as nearly coincident as possible with the horizontal magnetic axis connecting the pointed poles of the electromagnet previously described. The watch was enclosed in a ----ter's care with glass lids, and the distance between the poles was 1.6 cms (5/8"). The strength of the field in the absence of the watches at the magnetic axis was 4450 units and this was maintained practically constant during the experiment.####By means of a tapping key the time kept by the watch was compared with the clock and ---- by chronograph. After a time it was found that the ----- powerful magnetic stress operating on the steel minute hand caused the latter to a slightly after passing the poles, and consequently the measurements. It was therefore necessary to take a set of direct minute readings by chronograph and from the rate so obtained return through the past recorded observations so as to reclaim the set. This was done effectively as shown in the following table####[chart]####[page 58]####The means rate was thus an acceleration of ---- secs for minute or --- secs per hour or 2016 seconds per day. The record for the following day gives the rate per day at + 6 seconds showing no practical change from its previous value.####The experiment was repeated on the 27th August with watch # 2. Under the same conditions, the chronographs showed as losing rate of 2.2 seconds in 11 mins equivalent to --12 per hour or --288 per day the nominal rate being about 17 a day.####On slightly shifting this watch so that the magnetic axis passed through the hair spring at right angles but [excentiscally?] the rate was shown to be in the same field -2.8 secs --7 mins or --25 secs per hour or --600 per day####Watch No 12 was then substituted for No 2 and placed with its balance wheel axis coincident as nearly as possible with the magnetic axis. The chronograph record showed a loss of 0.6 seconds in 28 chronograph record showed a loss of 0.6 second in 28 minutes equivalent to a rate of --29 per day, this is practically the normal rate of the watch.####A series of measurements was then commenced with watch No 1 with the balance wheel and magnetic axis coincident, the field was altered by [9?] known amounts and the rates of the watch recorded on the chronograph in each. The results are shown on the accompanying curves --- The upper curve in the plots of the observations for the 27th day while the lower curve refers to a similar set repeated on the day following.####The conclusion deducible from these observations are that the direct influence of a powerful magnetic field traversing the hairspring is to cause the latter to decelerate but that the variations which different watches or the same watch in different positions present -- due to increased friction over the steel --- or making parts acting in ----- to the ----####[page 59]####In order to arrive ####[page 60]####His Remarks on the Temperature Records of the Watches.####It will be observed that the records of nos. 11 and 13 are omitted. No 11 was a private watch. No 13 was a good timekeeper but having been removed from its own gold case and [inserted?] in a jeweler glass cover case which did not fit it so well, the dial was found to be loose and to interfere with the motion of the hands. As this occurred several times during the test, it was decided to omit its record.####It will be seen that watches nos 9 and 15 failed to run at low temperatures.####[page 61]####a Test for the Magnetic quality of the hair sprung. The Palladium alloy of which the specimen springs experiments or have been composed manifests no magnetic action in a magnetic field until the strength of the latter approaches 3000 units when a portion of the filament will just show a slight tendency to set itself in the line of magnetic stress.####The Walthams non-magnetic spring taken from watch not proveson trial to be distinctly though only slightly magnetic. The reason for this is to be found in the fact that analysis shows a certain quality of iron to bepresent in its composition.####On cutting off 2.5 cm (1'') of this Waltham filament after straightening it and turning up [one?] and slightly so as to form a hook while the other end was allowed to attach itself to one pole of the chronomagnet the strength of the field being about 4000 units so thaqt the filament hangs naturally in the direction of the magnetic arcs, it is found to support 4.4 cms (1 3/4") of us 24 [G w G?] copper wire (0.16" d---) in addition to its own weights of 6.008grammes that is to say it require a total weight of 0.048 grammes to detach it from the pole.####Under the same circumstances on equal length of ordinary steel hair spring supports 12.8 cms or 51" of the same wire, thus requiring a total weight of 3.15 grammes to detach it####This Waltham spring is thus about 24 times less magnetic than steel under this above conditions.####[page 62]####As these results in themselves make it appear as though the watch were less injured when it had no cover than when the cover was over it, it was supposed that some difference in the relative arrangement of the moving parts in the field might account for the discrepancy. Accordingly another similar cover not magnetized was selected and this was fixed between the poles of the electromagnet and with it plane at right angles to the magnetic axis. The strength of the field was now gradually increased, and was measured both inside and outside the cover with the following results####[chart]####The deduction to be made is that the covers acted as a sheild for weak fields of ---- but it offers little protection to the influence of a strong field.####[page 63]####Appendix####Test for the shielding influence of five small ------- on red sheet non g----ts constructed on the ------- principle to enclose watch.####Diameter 5.8 cms (2 1/2")####Inside depth 1.9 cms (1/4")####A watch was placed inside one of these covers after it had been demagnetized and its rate compared. This comparison by chronograph as usual should that the watch was practically keeping mean time.####By means of a large electromagnet with the poles widely separated it was possible to place the covered watch in the field and measure the field intensity at the ----- time. The watch was left in the field dial up each occasion then removed, and tested for rate. The results are shown####[chart]####The watch which was now distinctly magnetic was now demagnetized, and the same test was repeated without any cover dial up####[chart]####
ments made with the -----sion watch soon made to envelop the watch, seem to show a decidedly lesser degree of protection then the Giles antimagnetic shield, and consequently would fail to preserve a watch except in comparatively weak magnetic field.####9th That a Paillard Non Magnetic Watch or p------ any watch whose hair spring is of non magneteable metal tends to ------- on being exposed to a magnetic field except or when the direction of the field####his is the plane of the hairspring (2) when the hair spring shares to find no metallic communication between its clamp and through the balance wheel and framework.####The ------ however may be apparently disguised diminished or were d----ed by the --- greater friction brought to bear on the magneteable s--- --- and working parts of the watch during the [perates?] of the magnetic stress.####I am Sir,####Yours faithfully####A.E. Kennelly.####[page 56]####8th That the experiments made with the -------- watch soon made to envelop the watch, seem to show a decidedly been degree of pretection then the Giles antimagnetic shield, and consequently would fail to preserve a watch except in comp----- f--- weak magnetic field.####9th That a Paillard Non Magnetic Watch or preserving any watch whose hair spring is of non magneteable metal tends to ----- on being exposed to a magnetic field except or when the direction of the field is in the plane of the hair spring (2) when the hair spring [stances?] to find no metallic communication between its clamps and through the balance wheel and framework.####The [peaimates?] however may apparently be disguised diminished or even [decreased?] by the [first?] greater friction brought to bear on the magneteable steel --- and working parts of the watch during the p----- of the magnetic stress.####I am Sir####Yours faithfully####A.E. Kennelly.####[page 57]####Aps--ai-####Comments made to determine the effect of a magnetic field on the rate of a watch whose brass spring is of non magenteable metal.####The watches experimented on were the Paillard no 1, 2, and 12. The ---- rates of their being steady and viable.####The first trial took place on the morning of the 25th August with the watch not placed pendant up with its balance wheel axis as nearly coincident as possible with the horizontal magnetic axis connecting the pointed poles of the electromagnet previously described. The watch was enclosed in a ----ter's care with glass lids, and the distance between the poles was 1.6 cms (5/8"). The strength of the field in the absence of the watches at the magnetic axis was 4450 units and this was maintained practically constant during the experiment.####By means of a tapping key the time kept by the watch was compared with the clock and ---- by chronograph. After a time it was found that the ----- powerful magnetic stress operating on the steel minute hand caused the latter to a slightly after passing the poles, and consequently the measurements. It was therefore necessary to take a set of direct minute readings by chronograph and from the rate so obtained return through the past recorded observations so as to reclaim the set. This was done effectively as shown in the following table####[chart]####[page 58]####The means rate was thus an acceleration of ---- secs for minute or --- secs per hour or 2016 seconds per day. The record for the following day gives the rate per day at + 6 seconds showing no practical change from its previous value.####The experiment was repeated on the 27th August with watch # 2. Under the same conditions, the chronographs showed as losing rate of 2.2 seconds in 11 mins equivalent to --12 per hour or --288 per day the nominal rate being about 17 a day.####On slightly shifting this watch so that the magnetic axis passed through the hair spring at right angles but [excentiscally?] the rate was shown to be in the same field -2.8 secs --7 mins or --25 secs per hour or --600 per day####Watch No 12 was then substituted for No 2 and placed with its balance wheel axis coincident as nearly as possible with the magnetic axis. The chronograph record showed a loss of 0.6 seconds in 28 chronograph record showed a loss of 0.6 second in 28 minutes equivalent to a rate of --29 per day, this is practically the normal rate of the watch.####A series of measurements was then commenced with watch No 1 with the balance wheel and magnetic axis coincident, the field was altered by [9?] known amounts and the rates of the watch recorded on the chronograph in each. The results are shown on the accompanying curves --- The upper curve in the plots of the observations for the 27th day while the lower curve refers to a similar set repeated on the day following.####The conclusion deducible from these observations are that the direct influence of a powerful magnetic field traversing the hairspring is to cause the latter to decelerate but that the variations which different watches or the same watch in different positions present -- due to increased friction over the steel --- or making parts acting in ----- to the ----####[page 59]####In order to arrive ####[page 60]####His Remarks on the Temperature Records of the Watches.####It will be observed that the records of nos. 11 and 13 are omitted. No 11 was a private watch. No 13 was a good timekeeper but having been removed from its own gold case and [inserted?] in a jeweler glass cover case which did not fit it so well, the dial was found to be loose and to interfere with the motion of the hands. As this occurred several times during the test, it was decided to omit its record.####It will be seen that watches nos 9 and 15 failed to run at low temperatures.####[page 61]####a Test for the Magnetic quality of the hair sprung. The Palladium alloy of which the specimen springs experiments or have been composed manifests no magnetic action in a magnetic field until the strength of the latter approaches 3000 units when a portion of the filament will just show a slight tendency to set itself in the line of magnetic stress.####The Walthams non-magnetic spring taken from watch not proveson trial to be distinctly though only slightly magnetic. The reason for this is to be found in the fact that analysis shows a certain quality of iron to bepresent in its composition.####On cutting off 2.5 cm (1'') of this Waltham filament after straightening it and turning up [one?] and slightly so as to form a hook while the other end was allowed to attach itself to one pole of the chronomagnet the strength of the field being about 4000 units so thaqt the filament hangs naturally in the direction of the magnetic arcs, it is found to support 4.4 cms (1 3/4") of us 24 [G w G?] copper wire (0.16" d---) in addition to its own weights of 6.008grammes that is to say it require a total weight of 0.048 grammes to detach it from the pole.####Under the same circumstances on equal length of ordinary steel hair spring supports 12.8 cms or 51" of the same wire, thus requiring a total weight of 3.15 grammes to detach it####This Waltham spring is thus about 24 times less magnetic than steel under this above conditions.####[page 62]####As these results in themselves make it appear as though the watch were less injured when it had no cover than when the cover was over it, it was supposed that some difference in the relative arrangement of the moving parts in the field might account for the discrepancy. Accordingly another similar cover not magnetized was selected and this was fixed between the poles of the electromagnet and with it plane at right angles to the magnetic axis. The strength of the field was now gradually increased, and was measured both inside and outside the cover with the following results####[chart]####The deduction to be made is that the covers acted as a sheild for weak fields of ---- but it offers little protection to the influence of a strong field.####[page 63]####Appendix####Test for the shielding influence of five small ------- on red sheet non g----ts constructed on the ------- principle to enclose watch.####Diameter 5.8 cms (2 1/2")####Inside depth 1.9 cms (1/4")####A watch was placed inside one of these covers after it had been demagnetized and its rate compared. This comparison by chronograph as usual should that the watch was practically keeping mean time.####By means of a large electromagnet with the poles widely separated it was possible to place the covered watch in the field and measure the field intensity at the ----- time. The watch was left in the field dial up each occasion then removed, and tested for rate. The results are shown####[chart]####The watch which was now distinctly magnetic was now demagnetized, and the same test was repeated without any cover dial up####[chart]####
Author
Mentioned
Date
1888-09-10
Type
Folder/Volume ID
LM111-F
Microfilm ID
109:148
Document ID
LM111117
Publisher
Thomas A. Edison Papers, School of Arts and Sciences, Rutgers University