Digitized by the Internet Archive in 2017 with funding from University of Illinois Urbana-Champaign Alternates https://archive.org/details/reportofsirwilliOOkelv THE giuct Into States Cable Compang. LIMITED. ym - — REPORT OE SIR WILLIAl THOlSOEjD-C.L., LL.D., F.R.S., F.R.S,E. AND MR. E. J. BRIIWELL, E.R.S., Member of the Council of the Institution of Civil Engineers. REP0E.T OE SIR WILLIAl THOISOI, L.O.L., LL.D., F.R.S., F.R.S.E. REPORT OE IR. E. JAIIESOE. LONDON : PRINTED BY WATERLOW & SONS LIMITED. gii'Mt ■ ' *> ■' ,• . -‘‘ii I .• D 'T 21st February, 1876. TO THE CHAIRMAN AND DIRECTORS OF THE DIRECT UNITED STATES CABLE COMPANY, LIMITED. GrENTLEMEN, In compliance with the request conveyed through Mr. Yon Chauvin (Managing Director), we have inspected portions of the cable of your Company with the object of enabling us to report to you as to the fractures which that cable has suffered since it was put to work on the loth of September of last year. It will probably be more satisfactory if we state, not merely the conclusions we have arrived at from our inspections, but also the details of the inspections themselves. In the course of these we were attended by your representatives — Mr. Yon CHAUYIN, „ BUDD, and „ BLANCHFORD. By the Contractors for the cable — Messrs. C. W. SIEMENS, and CARL SIEMENS; 4 and by their Engineers and Electricians — Mr. LOEFFLER, „ BRITTLE, Dr. HIGGS, Mr. SCHRAMM, „ LAUCKERT, and by Capt. TROTT,the captain of the cable ship Faraday,” We have to thank these gentlemen for the clear information they afforded us by their statements, and by their answers to our inquiries. Having thus been, as we believe, put into possession of a full knowledge of the circumstances connected with the fractures of the cable, so far as those circumstances were known to any of the above-named gentlemen, we directed our attention to the examination of the cable itself. The first piece examined we have lettered A.” This piece is stated to have been on the Irish or Eastern side of the first fracture, which fracture we are informed took place on the 27tli of September last, in latitude 45° 7' 12'' north, and longitude 54° 21' 24" west, and in a depth of about 70 fathoms of water. This portion of the cable has 18 sheatliing wires surrounded by two thicknesses of serving laid on and coated witli compound, and is of the construction referred to as Ho. 4633 in the specifi- cation under which the Contractors worked. The piece of cable forming the western side of the first frac- ture, we are informed, was not recovered, but the eastern side (A), which has been brought home and has been examined by us, affords conclusive evidence that the breakage has not been due to any decayed or imperfect condition of the cable, and also that it has not been due to the chafing of the cable against a rock, nor to any influence of an abrading or a crushing character, but that the breakage has occurred in a perfect cable, and through thoroughly sound metal, and has been caused by the whole having been torn asunder under a violent tensile strain. This is proved conclusively by the appearance of the ends of the sheathing wires, these ends being tapered down in the manner so well known as characteristic of the behaviour of good ductile metal in the act of breaking, such metal being reduced in its section b}?" extension under the strain after the elastic limit is passed and before final rupture takes place. With respect to the copper conducting wires of A ” their ends do not present the before-mentioned tapered appearance, but one indicative of having been separated by cutting. We are informed that this piece of cable was exhibited at the Conversazione of the Society of Telegraphic Engineers, held at Willis’s Booms, on the 21st December last, and that when the cable was sent there the copper wires and gutta percha core were in precisely the same condition as when first recovered from the sea, viz. : with a portion of the gutta percha core torn away from the main body and drawn a short distance along the conducting wires so as to leave a bared space therein, but that in the course of the evening some person unknown severed the wires between the main body of the gutta percha and the smaller piece beyond, and that to this circumstance is due the abrupt termination now presented by those wires. With respect to the manner in which the fracture took place, the appearance presented by the broken cable leaves no doubt whatever but that it has been subjected to a violent lateral strain caused by an implement such as the arm of a grapnel or the fluke of an anchor, which implement having been brought into con- tact with the cable on the western side of the fracture has run along it eastward driving the serving into the heap which is now accumulated on this piece (A) to the east of the fracture and forms there a thick mass round the cable for a length of 13 inches ; this accumulation of serving then arrested the further progress of the implement, as is proved by the mark on the iron sheathing left by the implement at the point where it was stopped by the accumulation of serving, and this stoppage 6 having been effected the final strain which broke the cable commenced. The next piece of cable we examined, we marked “ B.” This was stated to he a portion of a cable similar to “ A,” cut ofi from the part recovered (the remainder of that part having been used in the repair of the second fracture), and notwith- standing that this piece (B) is a portion of the cable which had been down for nearly a year and a half it is absolutely and entirely sound, in fact it has all the appearance of new cable, the external compound being in perfect condition. The next pieces of cable we examined we marked C” and D.” C ’’ we are informed was the piece on the Irish or eastern side of the second fracture,. and D ’’ the piece on the western side of the same fracture, which fracture occurred, as we are told on the 10th of December, last in latitude 44° 51' 45" N., longitude 58° 52' 0" "W., and in about 120 fathoms of water. The appearance of the two pieces C and D shows beyond doubt that they were on the two sides of one and the same fracture, and that there has been no loss of any portion from between them. The cable at this part is constructed with fifteen sheathing wires (No. 4G35 in the Specification) and is surrounded by two layers of serving with compound, as described in refe- rence to piece A.” An inspection of C and D shows that in the case of this second fracture as in that of the first, the breakage has not been due to any decayed or imperfect condition of the cable, and that it has not been caused by chafing, abrading or crushing, but that it has occurred, as in the first fracture, in a perfect cable and through thoroughly sound metal, and that the fracture is due to that metal having been torn asunder under violent tensile strain. The 15 sheathing wires in the specimens C and D have the the tapering down of the extremities already referred to as being shown in specimen A” and in the case of C and D the copper conducting wires being in the condition in wliich they were when taken up from the sea, exhibit in their ends the same characteristic feature of the elongation and of the diminu- tion in area of extensible material yielding under a breaking strain. C and D also show that the cause of the tensile strain has been again the action of an implement, such as the arm of a grapnel or the fluke of an anchor, by the slipping of which along the cable the outer serving has been dragged ofi* for a total length (taking the bared portions of the two specimens together) of 25 feet, and these pieces, C and D, further show that the cable was attacked either by two implements or by two successive attacks of one implement, as there is in D (the western side of the break), a strong indentation caused by such an implement, and in the neighbourhood of this indentation the cable has been distorted into an elliptical form, while close by the point of the rupture there is also in D the more serious mark due to the second grapnel or anchor, or to the second effort of the one grapnel, which latter indentation was certainly done at the time of the strain that produced the final rupture of the cable. We have already stated that with respect to the pieces C and D, as with respect to piece A, there is not the slightest indication of any deterioration of the cable, indeed, on each side of the bared part the outer serving and compound arc (as they are in A absolutely intact. On Monday, the 31st ult., we visited the Faraday,^’ lyiiig at Gravesend, and in the midship tank of that vessel we examined the cable, recovered on the occasion of the repair of the second fracture, this cable being of the 15 sheathing wire (No. 4635) kind. The cable was coiled in about four flakes near the bottom of the tank — the total length was stated to be about 12 knots — and we found that the upper flake comprised about 2l to 2|^ knots. This flake, which was exposed to our view, we minutely examined, and we found it to be thoroughly and completely sound, without indica- tion of deterioration of any kind or description, either to the outer serving or to the compound on the serving. In fact, it 8 was impossible to tell, except from the absence of the whitewash, usually applied to new cable to prevent one part from adhering to another, that it was not a newly manufactured cable coiled in the tank for the first time. With this qualification, however, that for a few of the coils near to the end, the outer serving was slightly chafed from having been dragged along the bottom in the act of being hauled in. Seeing how entirely satisfactory this top flake was, and observing that in the eye of the coil a similar satisfactory appearance was presented by the inuer turns of the three lower flakes, we did not think it neces- sary to have the cable uncoiled out of the tank for the purpose of examining its whole length. After our inspection in the tank, we had a portion of the cable made fast to a pair of powerful swivel hooks which are attached to the cable gear, and then caused the centre of this part to be pulled by one arm of a grapnel, the hauling rope of which was passed over the dynamometer ; a strain shown by the dynamometer to be 5 tons was then put upon the hauling rope of the grapnel, which, at the angle (about 90°) the spe- cimen of cable had then attained, represented a strain of 3.61 tons upon the cable itself. Beyond this the experiment could not be continued, as the blocks employed to put the strain on gave way, the cable proving too much for them. We directed specimens of the recovered cable to be sent to Messrs. Brown, Lennox, and Company, to be tested up to rupture in their chain cable proving machine, and the results obtained by them in three experiments varied from 7 to 7^ tons. Seven tons, therefore, may be taken as the power of resistance of the cable to a direct tensile strain. At the risk of repeating ourselves, we think it well to state definitely here, after recording this last test, that our experi- ments and examinations of the cable convince us it is one of an extremely strong form, that it has sufiered no deterioration whatever from its immersion for a period of about a year and 9 a half in the sea, and that the fractures have been caused by violence applied hy an implement and not by decay, and not by any abrasion, or rubbing, or any influence of that kind. The gutta percha of the cable at every part of the recovered specimens exposed to view was in thoroughly sound and perfect condition. Sir William Thomson’s assistant, Mr. Bottomley, by our direction, has tested in water at a temperature of 4^^, in the tank on board the Faraday,” the twelve mile length referred to above, and found its insulation to be 4,340 megohmns per knot. This reduced, according to the usual scale for gutta percha, gives 383 megohmns per knot at 75^, which proves it to be free from fault as might have been anti- cipated from the already stated excellent condition presented by the cable externally. One of the writers of this report (Sir William Thomson) tested this cable on the 16th and 17th September 1875, before you took it over from the Contractors, and found its electrical condition to be then perfect. Ten days after those tests were taken, the first rupture referred to above took place, and as we are informed at 5.17 p.m. Greenwich time (or 1.39 local mean time), suddenly in the middle of an acknowledgment. Torbay was working at the time to Ireland, and sent the “ Understand ” signal twice. Ireland received nothing further, but noticed immediately after the two Under- stands” had been received, violent throws on the galvanometer, and on testing, the cable was found to be to earth.” After the repair of this rupture, which repair was completed on the 5th November, the Company’s Superintendents tested regularly every Sunday morning, and the results of these tests wFich we have examiued show that the cable remained steadily in the same perfect electrical condition as that in which it had been before the rupture. With respect to the second rupture, that of the 10th of December, 1875, we are informed it took place at 7.45 p.m. Greenwich time (or 3.49 local mean time) and that Torbay was 10 working at the time to Ireland, and sent this here message ” and that nothing further was received, but immediately after the words here message ’’ had reached Ireland throws on the galvanometer were noticed, and on testing, the cable was again found to be to earth. This second rupture it is stated was repaired by the 9th of Janu- ary, 1876, when the tests again showed and continued to show the electrical condition of both sections of the cable to be still per- fect, and the complete series of tests made on the 8th, 9th and 10th of February by your own electricians, of which the details have been submitted to us, prove that the Ireland and Torbay section was electrically perfect in all respects at that time. We are informed a third rupture occurred on Sunday the 23rd Januarv, 1876, and at 3.1 p.m, Greenwich time, or 10.48 a.m. local mean time, and that this rupture was in the Torbay and New Hampshire Section. Neither station was working at the moment, but the operators were watching the instruments, and were exchanging signals every fifteen minutes, and while the Torbay clerk was thus watching he saw a sudden and violent throw on the galvanometer and the cable on testing was found to be to earth.” We have examined the Specification under which the Con- tractors, Messrs. Siemens Brothers, manufactured your cable, and find it provides in the most ample manner for excellence of material and workmanship, and also for continuous and rigorous testing by the Company’s Inspectors. We are informed by your officers that these test provisions were thoroughly carried out, and that the results obtained were so satisfactory that not merely the electrical conditions demanded by the Specification were fulfilled, but that in respect to insulation, nearly double that required by the Specification was in reality reached. These tests altogether proved the great care that was taken in the manufacture and the excellence of the result thereby attained. n Tlie laying of the cable was also conducted with the greatest care so as to avoid leaving in it any discoverable fault of insu- lation however minute. On three occasions while engaged on the deep sea portion of the cable its egress was stopped on account of faults which were very minute, two of these were hauled back and cut out on board the ship, while the third was cut out and left at the bottom. The two which were brought back have been marked with two notches and three notches respec- tively, these we have carefully examined and we find in each case the fault consists of a single exceedingly small air hole through the gutta percha, a hole so small as to be barely visible to the naked eye. On cutting down through the gutta percha to the copper core we found the wires composing it to be altogether undisturbed and unchanged, and to be perfectly central in the gutta percha, thus showing conclusively that the holes were not produced mechanically by puncturing inflicted by the wires of the copper core itself. There can be no doubt from their appearance but that the holes were produced in the course of the manufacture by minute quantities of air, which had been left in the compound before applying the gutta percha. The only other fault which occurred in the deep sea portion of the cable, we are told, was one which was found after the cable was recovered in May, 1875, and while paying out from the splice to complete the cable. This fault was cut out in September, after the cable was completed, but was not brought to the surface. It is to the scrupulous care which has been exercised to pre- vent any fault, however minute, from being left in the cable, that the chief delay in its completion was owing. This delay, however, has not been incurred in vain, for it is to the precautions which entailed the delay that the ex- ceedingly perfect electrical condition of the cable, as it now lies, is due. We think the contractors deserve great credit for their un- faltering determination, however deep the water and however O' 12 small the fault, to slur over nothing, and for the great efficiency of the means (material and personal) with which they carried on the operations, often in very heavy weather, and much of them in winter, and for their final success in giving you a thoroughly perfect cable. We have already stated it to be clear that both the first and second fratures of the cable, which alone up to the present time we have had an opportunity of examining, have been caused by a violent strain applied by an implement such as a grapnel or an anchor. The question now arises : How came a strain of this nature to be applied to the cable ? We are informed that the vessels chiefly found in these waters are fishing boats of about 80 or 100 tons, and that the greater number of them are American fore and aft schooners. It is in the highest degree improbable that vessels other than these fishing boats should anchor anywhere near the positions of the first and second fractures, that is, from 70 to 100 miles from shore, and in water of from 70 to 120 fathoms. The ques- tion thus seems to narrow itself to this : Is it possible that the ruptures have been produced by some of these fishing boats in the ordinary exercise of their vocation, anchoring in the neigh- bourhood of the line of the cable, and thereby breaking it, either in the process of coming to anchor, or in dragging the anchor afterwards, or in getting up or attempting to get up the anchor ? In the usual process of anchoring the vessel’s way through the water is nearly stopped before the anchor is let go. The contingency of being obliged to let go the anchor sud- denlv while there is still considerable way on the vessel could not occur in such situations as are now under consideration, and in so great a depth of water such a proceeding would be entirely useless, and would never be attempted. Further, if by any accident the anchor were let go when the vessel was going 13 rapidly tlirougli the water the anchor would not reach the bottom with the length of cable that would ordinarily be given to it. We therefore consider it impossible that any of the ruptures could have been caused by the sudden bringing up of a vessel immediately after casting her anchor. Supposing the anchor to have once reached the bottom, the force which a vessel of 80 or 100 tons dragging a light anchor such as those used by the fishing vessels on the Newfoundland Bank could bring to bear upon the electric cable must, except in the most severe gales, be very much less than that necessary to break the cable, and the effect of an anchor dragging to the line of the cable and then liooking it, would certainly be to bring the vessel up with but a. slight displacement of the electric cable along the bottom. Con- sidering the fact that the cable was laid at these parts with between 4 per cent, and 5 per cent, slack, and looking at the angle to which we found it bent in the neighbourhood of the second rupture, and taking the resistance to direct breaking strain as seven tons, we find that a force of about 4^ tons on an anchor or grapnel rope would be required to break the electric cable as we found it broken at the second rupture. In none but extremely bad weather could a vessel of from 80 to 100 tons put in deep water such a strain on her anchor. Assuming, however, a vessel to have hooked the cable with her anchor, and to ride to it without breaking it, as we have stated must be the case, if an anchor of one of these fishing vessels had dragged across the line of the cable, there then comes the consideration as to what would happen when such a vessel proceeded to get up her anchor. Bearing in mind again the 4 per cent, to 5 per- cent. slack, and the breaking resistance of 7 tons, we find that the strain upon the electric cable when raised to the surface from the greatest depth in which a rupture has occurred, namely, 120 fathoms (the second breakage) could scarcely ex- ceed If tons, or one-fourth part of the breaking resistance. 14 This estimate is corroborated by the strain shown by the dyna- mometer employed with the picking up gear. The foregoing considerations make it clear to us that if a fishing vessel having hooked the cable accidentally, brought it up to the surface and endeavoured to get the anchor on board, the cable could not be broken in the process. This conclusion is further corroborated by general experience, both of accidental and intentional grapplings of electric cables in similar depths. It may be suggested that the cable having been thus brought to the surface, it had been cut by an axe, as has sometimes been done to get rid of it, and to free the anchor, but the appearance of the ruptured ends of the cable, both of the first and second fractures, absolutely negatives such a suggestion. We have said that in none but extremely bad weather could a fishing vessel put a strain upon her anchor with such a depth of water that could have broken the cable. On examining the Meteorological Beturns, we find that on the occasion of the first fracture there was a very strong wind, but not one which we think would have been adequate to cause a fishing vessel riding to the cable to break it, although it is just possible the wind on that day might have been adequate to do so, but on the 10th of December, the day of the second fracture, the returns show that the weather was very fine, varying from light airs to calm, and under these circumstances, we have no hesitation in saying that it is absolutely impossible the cable could have been ruptured accidentally by a fishing boat pursuing its ordinary vocation. We desire here to call attention to the fact that from the summer of 1874, when the Nova Scotia section of the cable was laid to the summer of 1875 (during which time the cable, from the laying of the deep sea portion not being completed, was not in use), not one single breakage of the cable, as we are informed, occurred from any cause, nor did it even receive any injury to its insulation, for that remains perfect. 15 This immunity of the cable from rupture or damage of any kind during the greater part of two fishing seasons is evidence of the strong improbability of the repeated ruptures which have since occurred being produced accidentally by fishing vessels in pursuit of their ordinary calling, and is evidence also of the correctness of the views we have expressed upon another point, namely, that the cable is not exposed in the parts where the fractures have occurred to injury from large vessels, because such vessels have no occasion to anchor, and do not in the ordinary pursuit of their calling, anchor in 100 fathoms of water, and at from 80 to 100 miles from the shore. We have been asked by your Managing Director, whether Considering the direction and force of wind prevailing at the places in question and at the times of the ruptures, and con- sidering the position of the cable as laid, could, in your opinion, a sailing vessel at all have broken the cable accidentally on either occasion, or was it likely or unlikely that this should have taken place ? Could the cable, under these circunistances, have been broken on purpose by a sailing vessel on any one of the three occasions ? Would a steamer, in your opinion, have greater facilities than a sailing vessel for breaking the cable ? ” We have already answered the first part of this question with reference to the only class of vessels which would have anchored in such deep water. In answer to the last part, we have to say that the fishing vessels cables are certainly strong enough to break the electric cable if, as we are informed, they are from 7" to 9'^ manilla rope, as the breaking strain of 7 " manilla rope is as much as 14 tons, thus their tackle is in itself sufficiently strong, and it seems to us clear, that with wind enough to render a speed of 5 or 6 knots attainable by sail, a sailing vessel of 80 tons could, if handled for the purpose of doing so, break 16 the cable without lifting it to the surface, and that with a steam vessel so handled, the operation would be still more easy. We are, Gentlemen, Your obedient Servants, (Signed) WILLIAM THOMSON, The University, Glasgow, (Signed) F. J. BRAMWELL, 37, Great George Street, Westminster, S.W, 8IE WILLIAM THOMSON’S REPORT. On Wednesday evening, September 15tb, I arrived at Water- ville, and proceeded thence to the Cable Station at Ballinskelligs Bay. There your electrician, Mr, Ebel, met me, and showed me the instruments which he was ready to put at my disposal for the tests ; and Mr. Gravey, the Company’s superintendent, obligingly lent me a number of additional condensers which I desired for measuring the electrostatic capacity of the line. Having made preliminary arrangements, and learned that, by orders from London, the line was to be at my disposal from 7 till 10 next morning, I returned to Waterville for the night, appointing to meet Mr. Ebel at the station in the morning at 7 o’clock. About 8 a.m. on the 16th, after some preliminary trials of the instmments in connection with the cable, which showed strong earth-currents, I commenced testing for insulation with a battery of 20 cells, having its two poles constantly joined through a resistance of 20,000 Siemens units, but found so great disturbance by the earth-currents, that it was impossible to get a result. I first applied the battery for a quarter of an hour, zinc to line, then for seven minutes line to earth, then twenty minutes copper to line, and lastly, thirteen minutes line to earth. During the whole time a galvanometer, in circuit with the cable, showed strong currents alternately in the two directions, and varying from extreme nositive to extreme nega- 18 tive with great rapidity. To keep the readings within a conve- nient range I was obliged to shunt the coil so powerfully as to reduce the deflection to about what it would have been with a degree of sensibility proper for measuring the insulation resistance. The deflection was read OS' and written down every ten seconds during nearly all the time. A careful examination of these recorded results shows no sensible preponderance of current in the direction due to the battery, whether with copper to line or zinc to line ; and no perceptible difierence in the currents when the line was put to earth directly instead of through the battery in either direction. The currents observed were frequently ten times, and sometimes more than sixteen times, as strong as what I afterwards found to be the true leakage current, and the extremes were about as often in one direction as the other. The strongest current of all chanced to he in one of the periods when the line was simply to earth without battery. The sums of the readings taken during successive minutes show that the insulation resistance, whether with zinc or copper to line, cannot have been less than a megohm, and that it was probably not less than two megohms. I next measured the electrostatic capacity by the method which I described in a communication to the Society of Tele- graph Engineers, published in the Proceedings for 1873. I used three boxes of your resistance coils with 20,000 units on one side of the point put to earth and an adjusted resistance made on a box of 10,000 on the other side. The current from a well-insulated battery of 80 cells was kept flowing through these coils. With the condensers lent b}" Mr. Gavey, in addi- tion to your own, I had 80 microfarads in all. By means of the battery and resistance coils arranged in the manner de- scribed, the cable and condensors were charged oppositely in measured proportions, then connected together, kept so for about ten seconds,* and then discharged through the galvanometer to * Five reconds would have been quite long enough. 19 earth. Mr. Ebel’s insulation galvanometer with its ordinary magnetic adjustment was used, but its coil was strongly shunted to avoid over sensibility. Thus, after repeated trials, I found that when the cable and condensers were charged to opposite potentials in the proportion of 1,600 to 20,000, and then put in connection with one another, the charge in the cable was over- borne by that in the condensers ; but with the proportions 1,630 to 20,000 the' charge in the cable preponderated. Hence, about 1,615 to 20,000 would have given zero ; and, therefore, the capacity of the cable was ^ 8^ microfarads. that is, 991 microfarads (or *409 of a microfarad per knot, the length of the cable being 2,420 knots). I could have come much more closely to the exact proportion of the charges required to give the zero had the cable been at my disposal for half an hour longer, or had I perceived in time that one of the commutators which Mr. Ebel had left at my disposal could, in a few minutes, have been arranged to make the requisite connections by a simple manipulation instead of a somewhat cumbrous arrangement which I had extemporised. The quickness of this process, even with the cumbrous arrange- ment which I used, is such that it is much less disturbed by earth-currents than the ordinary tests for insulation or copper resistance. It is, in fact, disturbed only by whatever change there may be in the terrestrial potential along the line of the cable during the ten (or five) seconds between the insulated wire of the cable and the battery, and discharging the con- nected wire and condenser to earth through the galvano- meter. The last quarter-hour of the time for which the cable was at my disposal was spent in a somewhat hurried measurement of the copper-resistance. The line was found to be still greatly 20 disturbed by earth- currents. A battery of 20 cells was applied during 12 minutes, first zinc to line and copper applied to earth, and then suddenly reversed, and kept so till 10 o’clock (the time arranged for the conclusion of my tests), when signalling from the remote end commenced. During the whole 12 minutes there was a difference of potential between the Irish and Nova-Scotiau earths, varying rapidly in amount from a least minimum of 5 cells to a greatest maximum of 18 cells, but always in the same direction : — the Irish earth positive relatively to the I^ova-Scotian earth. The ordinary bridge method could have given no result at all in so disturbed a con- dition of the line ; but the simple method of defiection (the only proper method for measuring copper-resistance in a submerged cable), in which is observed the difference of the readings im- mediately before and quickly after reversal of the battery; gave an approximate result, which in round numbers I took as 7,300 Siemens units. The cable being offered to me again from midnight till 2 a.m, on the 17th, I made another series of tests at that time, for the main object of measuring the insulation-resistance. I found the line in a much less disturbed state, and was able to make a perfectly satisfactory insulation test by the ordinary galvano- meter method. I applied, however, also a new method which (no electrometer being available) I had planned to meet the contingency of the line being disturbed by earth currents so much as to render the ordinary test unsatisfactory, but not so much as to vitiate an electrometer test. This method, wliich I think may bo found generally useful for testing submerged cables when an electrometer is not available is as fol- lovv^s : — 1. Apply the ordinary test by battery and galvanometer for a certain time. 2. Insulate the cable for a certain time and then shunt the 21 galvanometer to prepare for No. 3 (unless you have conve- niently available a second galvanometer suitable for is- charges). 3. Instantaneously re-apply the battery, through the insula- tion galvanometer properly shunted (or a special discharge galvanometer), to the cable, and observe the maximum of the sudden deflection produced. 4. Go on repeating Nos. 1, 2, and 3 as long as you think proper, according to circumstances. 5. To determine the proper ballistic constant of the galvano- meter for utilizing the observed result of No. 3, find the maxi- mum of tJie sudden deflection which takes place when a sudden change of electrification is produced by instantaneously chang- ing by a small measured difierence the potential of one electrode of the galvanometer, the other electrode being in connection with the cable. 6. The change of potential which, in the operation of No. 5 would give the same deflection as that observed in No. 3, is equal to the change of potential which the conductor of the cable has experienced during the time when it was left insulated according to No 2. Hence calculate the insulation-resistance in ohms or megohms as in the ordinary electrometer method, when the electrostatic capacity of the cable is known. At 12h. 2m. on the morning of the 17th, the 20-cell insulation battery (with its poles again, as on previous occasions, joined through 20,000 Siemens units) was applied, zinc to cable through the insulation galvanometer with a shunt of 5,000 Siemens units on it. Then, commencing at 12h. 2m. 50s. the galvanometer indication was read and recorded every ten seconds till 12h. Gm., when the cable was insulated during a minute, according to No. 2 of the directions above, and a shunt of 30 substituted for the 5, 000. At 12h. 7m. the battery was instantaneously re-applied, the throw of the galvanometer 22 observed according to No. 3, and tbe shunt of 30 removed, and 5,000 re-applied. The battery was kept on till 12h. 8m., when the cable was again insulated for a minute, the galvanometer shunted with 50 (instead of the 30 used the first time), and the operation of No. 3 repeated. This process of re-applying the battery and re-insulating the cable, in alternate minutes, was continued till 12h. 26m. Then an interval of five minutes was spent in determining, according to No. 5, the proper ballistic constant of the galvanometer, by applying alternately full power and -lu- of full power of the insulation battery ; the change from one power to the other being made in each case as instan- taneously as possible. Lastly, the shunt of 5,000 was re applied at 12h. 31m. for insulation-test, and one more period of the alternating process performed from 12h. 32m. to 12h. 34m., when the cable was put to earth to prepare for insulation-test with cop- per to line. Either three or four, generally four, galvanometei readings for ordinary insulation-test were taken at intervals of ten seconds in the second half of each minute during which the battery was applied. Twelve galvanometer readings taken at ten seconds intervals during the second and third minutes of the electrification gave for mean deflection 127, and the readings taken during the second halves of the fourth, eighth, tenth, twelfth, fourteenth, sixteenth, eighteenth, twentieth, twenty- second, and twenty-fourth minutes gave for mean deflection 82*1- The sensibility of the galvanometer in the condition in which it was used for these readings was such that a deflection of 290 would have been given by the actual battery, with a resistance of 10^ Siemens units. Hence, the insulation resist- ances proved by the mean observed deflections were as fol- lows : — Mean deflection Insulation resistance. 127 (2nd and 3rd minutes) 2*28 x 10® | Siemens 82*1 (4th, 6th, ... 24th) 3*54 x 10® J units. 23 The new method described above gave the following ballistic deflections or throws ” : — End of 5th minute 70 divisions. -V 7th ,, ... 102 ?? -V 9th ,, ... 102 if 11th ,, ... 109 if 13th ... 57 if 15th ,, ... 52 » j 17th ,, ... ... 92 if J? 19th ,, ... 102 if 21st ,, ... ... 110 if J? 23rd ,, ... ... 102 if Mean ... 89*8 Say ... 90 The ballistic deflection due to instantaneously changing the potential by of that of the insulation battery, in accordance with the rule of No. 5 above, was found to be 112 divisions This is IJ time the preceding mean throw, which therefore showed a change of potential equal to of that of the battery. Hence the mean of the falls of potential in the ten alternate minutes during which the line was insulated was of the potential at the beginning of each of them, or (nearly enough) of the mean potential during the minute. Therefore, the loss was at the rate of -gV minute, or second. Now, I had found the electrostatic capacity of the cable to be 991 microfarads. Hence the insulation resistance proved by this mean result is or 3*027 megohms, or 3, 170,000 Siemens units This agrees quite as nearly as could be expected with the 3,540,000 Siemens units deduced from the means of the galvanomer deflections during the alternate minutes when the battery was in action, as described above. At the conclusion of the zinc to cable ’’ test, the cable was put to earth and kept so for two minutes, till 12’36, when a similar series of tests with copper to cable was commenced, always with the same battery of 20 cells. These tests were much disturbed by another storm of earth-currents (not quite so severe however as that of the preceding morning) which came on very suddenly about the fourth minute of electrifica- tion, and nearly stopped the leakage current (giving an apparent insulation-resistance of 7,000,000). The new ballistic test was then applied and continued in alternate minutes as before. The first ballistic deflection gave an apparent resistance of 5,000,000, and the second actually showed an increase of potential (rela- tively of course to the Ballinskelligs earth) during the minute of insulation. Then came ten minutes of comparative tranquillity, till 12h. 52|m. when the leakage current from the battery was rapidly reduced to zero and reversed, and a quick succession of violent pulsations supervened for about a minute and a half, throwing the spot of light alternately off scale to right and off scale to left, at irregular intervals of ten or fifteen seconds. About 12*56, there being still great deflections, but not so rapid pulsations, a shunt was applied which allowed the amounts of the deflections to be observed, and showed them to range fre- quently from ten to forty times the proper leakage current, some in the contrary direction to it, and some in its own direction* The disturbance diminished gradually till Ih. 7m. a.m., when the cable was discharged to prepare for measurements of capacity and copper resistance. Notwithstanding the very disturbed state of the line the means of the regular observations taken between 12*39 and 12*53 gave satisfactory results in respect to insulation resistance. Thus the mean of 24 deflections observed in the ordinary galvanometer test during that interval was 112*2, which gave for insulation resistance 2,585,000 Siemens units, this being for the time from the end of the fourth minute to the end 25 of the sixteenth minute of electrification. The ballistic defiec * tions observed were : — End of 5 th minute . . + 52 divisions jj 7th . - 10 »5 }f 9th . + 80 yy V 11th . +160 yy 13th a . + 92 yy 15th . +102 yy 17th yi . + 62 yy 538^7 Mean . . 77 This with the ballistic constant, determined in the manner ex- plained above, gives 3*52 megohms, or 3,690,000 Siemens units, for the insulation resistance. Ths measurement of electrostatic capacity described above was next repeated, and the previous result confirmed, but there was not time to attain to more minute accuracy in the ad- justment. Lastly, the copper resistance was measured by the simple gal- vanometer method. The insulation-galvanometer, quickened three or four fold by a magnectic adjustment (which I had used also in the insulation- tests), and with a shunt of 20 Siemens units on its coil, was put in circuit between line, battery, and earth, and the deflection was observed and recorded every ten seconds during the whole time of the test, which was from Ih, 36|m. to ] h. 58m. As was to be expected, large and rapid variations of the deflection were continually taking place on account of earth- currents. The direction of the earth-current was from east to west the whole time, as was shown by the copper ” current being always greater and the zinc’ ’-current less than the true mean concluded from the observations. It increased gradually (but with some slight backward pulsation) from the beginning 26 (Ih. 26 Jm.), when its amount was that due to a difference of potentials between the Ballinskelligs and Torbay earths, equal to T7 of a cell (one cell and seven-tenths), till the end (Ih. 58m.). when it was more than five times as strong, and corresponded to nine cells ; the Irish earth positive relatively to the Nova- Scotian earth the whole time. To measure the copper resistance a time of comparative tran- quility was chosen, a reading taken, and then as quickly as possible the galvanometer short-circuited, the battery reversed, the galvanometer circuit re-opened, and a fresh reading taken. Half the space travelled by the spot of light from the hrst reading to the second is taken,* as being the deflection which would be produced by the battery applied in either direction were there no earth-currents. This was done seven times, and the half-ranges found were as follows : — 235 231 22H 2Mi 231 235 230 Mean . . 232*3 * Supposing there to be no instrumental error, the sole error in this pro- cess is that depending on the change of earth-current between the first and second reading, hence the importance of quickness, and the value of the dead-beat” galvanometer for such observations. So far as the cable is concerned five seconds (as I find from my mathematical theory) is amply sufficient from the instant of reversal to the second reading to secure that there be no sensible error on account of the current not having become nerfectly uniform from end to end. But far more than five seconds is req aired to get the second reading, on account of the swinging of the galvanometer needle when the customary “ astatic mirror” is used. With the dead-beat galvanometer the second reading is easily taken within five seconds of the first. 27 At 2h. 2m. I found that the same battery applied in the two directions through the galvanometer and 7,300 Siemen’s units gave 232 divisions on one side of zero and 233 on the other — ■ mean 232*5. Hence the copper resistance to be inferred from the observations is 7,300 X 232*5, 232*3 or 7,306 Siemens units. Summary of Tests of Sept. 16 and Sept. 17. Insulation Resistance of whole cable of 2,420 • knots in 2nd and 3rd minutes 2J millions Siemen’s units, or 5,445 millions per knot. from 4th to 24th minutes. 3 J millions, or 8,470 millions per knot. Copper Resistance of whole line 7,300 Siemen’s units, or 3*02 „ „ per knot. Electrostatic Capacity of whole line ...991 microfarads, or •4,095, say *41 per knot. Throughout the preparations and observations re- quired for the tests which I have now described, I received skilful and efficient assistance from your electrician, Mr. Ebel, and his assistant; and I desire to take this opportunity of expressing through you my thanks for the patience and care with which they went through the somewhat irksome and tedious series of operations which I had to ask of them. In conclusion, I am glad to be able to say that my tests proved the cable to be in perfect condition as to insulation, and showed its electrostatic capacity and copper resistance to be so small as to give it a power of transmitting messages, which, for a transatlantic cable of so great length, is a very remarkable as well as valuable achievement. (Signed) WILLIAM THOMSON. The Univeesity Glasgow, Sejn. 23 , 1875 . REPORT OP MR. JAMIESON. EEPOET ON TESTS OF DIRECT UNITED ST AT ES CABLE, TAKEN AT BALLINSKELLIGS BAY STATION, February 8^4, ^th and lOth, 1876. Tuesday, 8tli Februaky. All the necessary instruments and batteries having been kindly placed. at my disposal by Mr. Gavey, the Company’s Superintendent, some time was spent previous to testing the cable in comparing the different resistances to be used in the tests. The cable was then earthed at Torbay from 7 to 8 a.m., and a dead beat galvanometer properly shunted, and 20 cells were connected up for measuring the copper resistance of the cable by the Direct Deflection method. As, however, equal deflections were not obtained on each side of the scale with a constant resistance the tests made were rendered worthless, and some time had to be spent in properly adjusting the mirror. Ai 7.30 a.m. connections were made for measuring the copper resistance by the Bridge method, and the following readings were obtained — zinc and copper applied alternately — the one as soon as possible after the other : — 31 Zinc 7325 Copper ,, 7323 >> „ 7324 „ 7318 „ 7315 7318 Zinc 7318 7318 „ 7319 7315 „ 7320 7317 „ 7318 7320 „ 7319 Mean resistance, 73 18’ 8 or 3*0209 per knot. Copper 7318 7319 7316 7319 j? 7318 During the remaining few minutes the strength of the earth current was compared with one of the testing cells. Deflection through cable by E.C.=455 degrees. „ „ 7319 su. by 1 cell=l 10 „ Therefore the earth current ^4*14 cells and positive in direction. WEDNESDAY, Feb. 9th. The cable was insulated at Torbay from 7 to 8 a. m. and con- nections were made for measuring the electrostatic capacity of the cable according to the method adopted by Sir William Thomson when testing the cable in September last. 80 cells. 80 cells, 80 micofarads and an astatic galvanometer were used, the connections being as shown in the diagram. The resistance which gave the least deflection was 1,620, but by no arrangement of the variable resistance could no deflection be produced except by using a very delicate shunt for the gal- vanometer. 32 Taking then thic resistance 1,620 the electrostatic capacity of the cable is mcf.=987’6 microfarads, or 4,077 per knot. Altogether ten tests were made before the approximate bal ance was obtained, and between each test the cable was earthed for two minutes. The ten adjustments of the variable resistance were 1,615, 1,650,^1,640, 1,630, 1,625, 1,624, 1,622, 1,620, 1,619, and 1,620. At 8.15 a.m, the cable was again insulated at Torbay till 8.45 a.m. in order to measure the insulation resistance of the cable. As the earth currents were very weak at the time the direct deflection method was adopted, and for that purpose the astatic galvanometer (with a shunt of value 10) and 20 cells were used. The following were the deflections obtained at the difierent periods of observation : — IT. 8T6 a.m. copper current applied. M. s. Deflection. 8 17 0 A.M. 10 20 o CO }J jj 40 n 50 8 18 0 350 300 ' 310 310 270 ' 285 265 . Mean 350. 290. 8 „ 10 „ 20 „ 30 „ 40 50 19 0 }7 5J 280 ) 270 245 200 200 220 236 . 33 H. 8 M. 19 s. 10 55 Deflection ... 260 1 Mean. JJ 55 20 5 5 ... ... 200 1 i • I 55 30 55 . . . ... 20o 1 f 55 213. 55 40 55 . . . ... 210 55 50 55 . . . ... 240 s 20 0 5 5 .. 170 , ) .. 55 10 55 ... ... 190 5> 55 20 55 ... 215 • j 55 30 .. ... 220 ! ,5 208. 57 55 40 55 ... 225 55 55 50 55 . . . ... 210 8 21 0 55 ... ... 190 55. 55 10 55 s. ^ o 00 I— 1 ! 55 55 20 55 ... ... 200 ,• j 5 j 30 55 ... ... 200 ' 55 55 40 . . . ... 200 ' „ 202. 55 55 50 ... ... 210 8 22 0 55 ... ... 220 / f 55 55 10 55 . . • ... 170 ^ 55 55 20 55 . . . ... 180 5 5 55 30 55 . . . ... 190 ) .. 55 40 55 ... ... 230 „ 198. 55 55 50 55 ... ... 210 8 23 0 55 ... ... 210 8 23 0 55 to Cable to earth 8 30. 8 30 0 zinc current applied 55 31 0 55 ... 370 ,, 370. 55 55 10 55 ... ... 310 55 55 20 55 . . . ... 325 5f 55 30 55 ... ... 350 ,, 299. 55 55 40 55 ... ... 310 [ 5» 55 50 55 ... . . . 255 55 32 55 55 ... ... 245 j 3 34 II. M. .< . Deflection. 8 32 .10 ?> . . . . . . 270 jj 20 j? . . . 270 .. 30 33 ... 225 .. 40 33 ... 250 ;? 50 33 . . . 215 • 5 33 33 ... 245 I .tj ?» 10 3:- ... 275 \ ?> 20 33 ... 190 .1) ,, 30 33 195 <5 j? 40 33 . . . 210 ) J? >5 50 ., ... 240 JJ 34 j? 33 ... 250 10 33 ... 240 jj 20 „ . . . 220 ,, 30 33 . . . 220 >> 40 j. . . . 230 \ / ,, 50 33 . . . 210 35 33 •• 190 , ^ .. 10 ,, ... 195 .V 20 33 . . . 200 j? 30 33 ... 205 }> 40 ., ... 210 f .. .. 50 200 1 1 ;? 36 33 ... 205 I /' ?> jj 10 33 ... 200 3} 20 33 ... 220 1 >5 30 33 210 [ 40 33 . . . 195 .. V 50 33 . . . 200 ?5 37 33 . . . 190 1 Mean. j? 246 . 227 . 218 . 209 . 202 . 35 A deflection of 406 degrees was obtained with zinc and copper from 20 cells, through 20,000 su, and the galvanometer, with a shunt of value 1,000. Taking then ^the deflections after one minute, and the means during the remaining six minutes, the following results are obtained : — Period of deflection used in calculation. Insulation resistance in millions, S.U. 1 C 0 P P E E. Zinc. Whole length. Per knot. Whole length. Per knot. End of 1st 1 minute.... 2-32 5,620 2-2 5,329 1 During 2nd . 2-8 6,783 2'72 6,589 During 3rd.. 3-44 8,334 3-3 7,994 During 4th . 3-81 9,230 3’o8 1 8,673 During 5th . 1 3*9 9,448 1 3’7 8,963 During 6th . 4-02 9,739 3-89 9,424 1 During 7th . 4-1 9,932 3-96 9,593 The cable was then earthed at Torbay, from 9 to 9.15 a.m., and connections were made for measuring the copper resistance of the cable by the direct deflection method, the dead beat galva- nometer, properly shunted, being substituted for the astatic. Twenty cells were used, and the following deflections were read from zinc and copper alternately — the one as soon as pos- sible after the other : — 36 Z. 197 191 C. 208 210 192 192 210 210 Mean of 194 196 211 210 Deflections, 192 194 208 208 201*3. 192 195 210 206 Substituting a variable resistance for the cable it was found that 7350 j Bu. gave 195 degrees Z. and C. 7340 197 7330 198 7320 200 7312 201 Therefore 7312 su. = Copper Resistance of whole length or 3*018 „ = „ per knot. The deflection caused hy the earth current with cable galvanometer and earth in circuit was 256, and positive in direction as compared with 110 from 1 cell, 7312 su., and the galv. in circuit. Therefore the earth current = 2*33 cells, THURSDAY, 10th Feb. The cable was earthed from 7*15 to 7*45 a.m,, at Torbay, and the copper resistance of the cable was measured by the direct leflection method with the same connections as on the previous morning. The following readings were obtained. Zinc and copper applied alternately, the one as soon as possible after the other : — Z. 185 195 C. 255 230 198 210 240 240 199 189 245 252 190 192 247 243 205 200 235 246 195 189 250 255 Mean deflection 220.2 37 Substituting a variable resistance for the cable it was found that — 7320 su. gave 218 Z. and C. 7310 „ „ 220 „ „ Therefore 7310 su = copper resistance of whole length or 3’0176 „ „ per knot. Cable w'as again earttad at Torbay from 8 to 8.30 a.m., and connections were made f©r measuring the copper resistance of the cable by the Bridge method. The dead beat galvanometer and 20 cells were used. The following readings were obtained, Zinc and copper applied alternately. Z. 7315 C. 7318 7312 7315 7312 7310 7310 7312 7315 7312 7315 7315 7315 7315 7318 7318 7315 7315 7312 7312 Mean 7314 or 3’0193 su. per knot. The deflection caused by the earth current with cable, galva- nometer and earth in circuit was 295, and positive in direction, as compared with 101 with 1 cell 7310 su., and galvanometer in circuit. Therefore the earth current =2*92 cells. 38 SUMMARY OF TESTS. LENGTH OF CABLE, 2422‘565 KNOTS. Feb. Wi, Copper Besistance by Bridge Feb. 9^//, Electrostatic Capacity Insulation Besistance by direct deflection during Copper Besistance by direct deflection Feb. l^th, Copper Besistance by direct deflection by Bridge (Signed) whole length 7318.8 su. per knot 3-0209 „ whole length 987-6 mic. per knot •4077 „ v/hole length per knot, end of millions millions 1st min. 2*26 su 5475 su. 2nd 2-76 6686 3rd 3*37 8164 4th 3*69 8939 5 th 3-8 9205 6th 3*95 9569 CO cp 4ih 9763 whole length 7312 su. per knot 3-018 „ whole length 7310 su. per knot 3-0176 whole length 7314 su. per knot 3-0193 FIFE JAMIESON. WATERLOW ATJD SONS LIMITED, i