PUBLIC RECORD OFFICE
Reference :-
C.O. 885
6
PUBLIC RECORD OFFICE, LONDON
ALLY WITHOUT PERMISSION OF THE
BE REPRODUCED PHOTOGRAPHIC- COPYRIGHT PHOTOGRAPH-NOT TO
260
PACIFIC CABLE COMMITTEE :
copper and gutta-percha that should be used in the core. cables may be taken as a guide:—
The following data of long submarine
Core.
Length, Knots.
K. R.
400 copper.
1875. Ireland-Nova Scotia
360 gutta.
2,564
7.81 x 108
350
1892. Penzance-Nova Scotia
300
"
2,563
7.38
"
350
1881. Do.
do.
2,518
7.18 11
300
+
350
1879. Brest-St. Pierre -
2,302
6.53
300
"3
12
500
1894. Ireland-Nova Scotia
2,101
4.22
320
事
01
250
1879. Aden-Zanzibar
1,908
6'30 21
250
"
400
1873. Valentia-Newfoundland
33
1,876
3.68 13
400
250
1884. St. Vincent-Pernambuco
250
"J
1,862
5.35
32
400
1891. Aden-Bombay
1,850
3.74
300
官
650
1894. Valentia-Newfoundland
1,847
'2:41
رو
400
400
1874. Do.
do.
1,837
3.38
13
400
200
1,389
3.88
1891. Madras-Penang-
"1
180
130
1890. Australia-New Zealand
1880. Java-Australia
1,322
5.30
130
107 140
D
1,131
3.98
23
The speed of signalling through a cable varies inversely as the K.R. of the line. The K.R. of any submarine cable is obtained by multiplying together the total electrostatic capacity in micro- farads and the total conductor resistance in ohms.
This product for the cables tabulated is given under the column headed K.R., and these figures show that this value does not in any existing cable exceed 7-81, whilst in most of them it is con- 860 copper would give a K.R. 78, but we are of opinion that in a cable of this great length, where the depth of water exceeds 3,000 fathoms, some sacrifice must be made in order to keep the weight of the cable within practicable limits. The experience that we gained in laying the 1894 Valentia-Newfound-
650 land cable, which has a core of 400 (the largest yet laid) showed us that, although a cable with that weight of core could easily be paid out in 3,000 fathoms, the atrain in picking it up from that depth would approach the limit of strength that a cable manufactured with the best steel wire would possess.
siderably leas. In a length of 3,650 miles a core composed of 520 gutta-percha
650 copper
We have therefore specified for a core of 400 gutta-percha, which would, when' laid in a length
of 3,650 miles, have a K.R.=94, which, estimated on the basis of the working of existing cables, would allow of the transmission of 70 letters per minute.
We have given the K.R. of the various existing cables in preference to making a definite state- ment as to their speed of transmission, the latter being governed largely by the methods of working and the appliances adopted.
Moreover the speed which is usually spoken of in connexion with telegraph lines is misleading, it being calculated from the attainable speed with press work, counting five letters as a word, whereas the actual speed of paying words in code traffic does not amount to more than about half this.
The weight of the main cable in air would be 2:01 tons per mile, and the weight in sea water 1-13 tons. The estimated strain that would be put upon the cable in picking it up at a speed of
CORRESPONDENCE,
261
half a mile an hour in moderate weather from a depth 3,000 fathoms would not be more than 6 tons. The breaking strain of the cable would be about 8 tons.
The quality of the steel wire that we have specified goes as far in the direction of strength as can safely be done without loss of elasticity. The electric welding of the wire is important; hand- made welds in small steel wires are very uncertain, and brazed or soldered joints, although strong at first, lose all their strength after a few years' submersion.
The covering of each wire with a good elastic waterproof compound and tape is essential to prevent the sea water from corroding the steel; we consider that to simply tar or black varnish the wire is not enough to ensure its retaining its strength after some years' submersion.
I am, &c.,
GEORGE HENRY RICHARDS, Admiral,
417
Enclosure in No. 1.
TELEGRAPH CONSTRUCTION ANd Maintenance Company, Limited.
PACIFIC CABLE.
Chairman.
Specification of proposed Types to be laid between Vancouver and Funning Island.
Core.
(a) The conductor to consist of a central copper wire, 122 of an inch in diameter, surrounded Conductor. by 12 copper wires, each 041 of an inch in diameter, the completed conductor to weigh 650 lbs. per nautical mile, or within 5 per cent. thereof, but the average weight per nautical mile of the conductor shall not be less than that specified. The resistance per nautical mile of the conductor at a temperature of 75° Fahrenheit shall not be more than 1.9 ohms.
(b.) The conductor is to be insulated with three coatings of gutta-percha of improved inductive Insulator. capacity, prepared according to Mr. Willoughby Smith's system, alternating with three coatings of Chatterton's compound, and to weigh 400 lbs, per nautical mile, or within 5 per cent. thereof, but the average weight per nautical mile of the insulator shall not be less than that specified. The resistance of the completed core to be not less than 250 megohms per nautical inile after one minute's electrification, when tested at a temperature of 75° Fahrenheit, after 24 hours' immersion in water, 14 days after manufacture, and the average inductive capacity per nautical mile throughout the entire length is not to exceed 43 microfarads.
·
(c.) The core of Types A. and B. to be covered with Clifford's patent brass tape sheathing for Sheathing. protection against the ravages of insects.
(d) The core of all the types to be served with a good and sufficient serving of jute yarn, Serving. steeped in cutch or other preservative mixture, and applied wet, the yarn for the deep sea type to be fine apun, of even diameter, and of good quality.
Outer Coverings.
coveringe.
(e) Type A-Type B. to be served with tarred jute yarn, and again closed with 14 galvanised Outer BB iron wires, No. 1 B.W.G., equal to 300 of an inch when galvanised, or within 2 per cent. thereof. The wire to be soft, and of good quality.
(f.) Type B.-The served core to be covered with 12 galvanised BB iron wires, No. 6 B.W.G., equal to 200 of an inch when galvanised, or within 2 per cent. thereof. The wire to bear a breaking strain of not less than 30 tons to the square inch, with an elongation of not less than 10 per cent., and to stand not less than 10 twists in a length of 6 inches.
(g) Type D.-The served core to be covered with 18 galvanised steel wires, each wire being well covered with a preservative compound and taped. The steel wires to be No. 14 B.W.G., equal to 083 of an inch when galvanised, or within 2 per cent. thereof, and to bear a breaking strain of 1,100 lbs., or equal to 100 tons per square inch of sectional area of the steel, with an elongation of not less than 4 per cent. The wire to be capable of being bent round its own diameter three times, and unbent three times without breaking. The wire to be in bundles of not less than 2 cwt., and to have but one weld in each bundle. The wire to be electrically welded.
(h) Before being used for the sheathing of Types A. and B. the galvanised iron wire is to be heated in a kiln or oven just sufficiently to drive off all moisture, and whilst warm is to be dipped into a hot compound of coal tar and pitch mixed in approved proportions.
Outside Serving.
(i.) Type A., manufactured as above, to be covered with two servings of jute yarn, laid on Outside spirally in opposite directions, alternately with two coatings of Clark's compound.
(j.) Types B. and D., manufactured as above, to be covered with two of Johnson and Phillips' patent tapes, laid on spirally in opposite directions, alternately with two coatings of Clark's compound.
38, Old Broad Street, London, E.C.,
0 92688,
July 3, 1896.
LI
serving.
262
PACIFIC CABLE COMMITTEE:
No. 2.
DEAR SIR,
SIR H. C. MANCE to MR. MERCER
32, Earl's Court Square, S.W., July 4, 1896.
I REGRET that my absence from town has prevented ine from sending you the promised memoranduin on the Pacific Cable Scheme.
Should you You will see I have only referred to one or two points which have first to be settled. decide to go on with the business, there are many others which require careful consideration.
Whether the contract is vested in a Company or a Commission, you will, of course, provide that the cable is kept in working order for a certain time at the expense of the contractors.
Yours, &c.
HENRY C. MANCE.
Enclosure in No. 2. PACIFIC CABLE.
MEMORANDUM by Sir HENRY C. MANCE, C.I.E., Member Institution Civil Engineers, Vice- President Institution Electrical Engineers, formerly Engineer and Electrician to the Government Persian Gulf Cable, and now Director of the West African Telegraph and South American Cable Companies.
I have carefully inspected the chart of the Pacific Ocean and considered the suitability of the proposed route for the Pacific Cable.
Speaking generally, the soundings which have been obtained appear to me to indicate that the bottom of the Pacific is very suitable for a submarine cable, indeed quite as good as that of the Atlantic; there is nothing which suggests to me that there would be any difficulty in laying, or recovering if necessary, a cable of suitable design.
At the same time the project is one which should be very carefully considered, but I feel sure that if dealt with cautiously and prudently there will be no exceptional engineering difficulties to be
overcome.
Our South American cable is laid in depths which in places must closely approximate the soundings which are obtained in the Pacific. Our experience tells us that, a good cable once properly laid, the deeper the water the fewer the interruptions, at the same time it is encouraging to know that repairs have been effected in depths of 2,700 and 2,900 fathoms,
With regard to the durability of the dielectric of a cable, I may say that I have had both india- rubber and gutta-percha under my close observation for over twenty years, and I give it as my opinion that, providing the material is carefully selected and properly manufactured, the question of durability need not be considered: faults in manufacture will of course have to be carefully guarded against, they are happily few. Out of 77 repairs executed by me in ten years, only two faults were due to faulty manufacture, both of these faults would no doubt have manifested themselves immediately had the cable been laid in any great depth of water.
I have carefully estimated the probable working expenses and consider that 30,000l. per annum would provide for administration in London, operating staff at six stations, and all expenses incidental to a Submarine Telegraph Service.
In framing this estimate I have considered the class of clerk that would be required, many of the operators would have to be the best men obtainable, and it would require some time to collect them. I have not checked the various estimates which have been given as to the cost of a cable, as the Once having decided on the dimension of total may vary so greatly according to the type selected.
the core and deep ses type, the calculation for speed, weight, tonnage required, cost of manufacture and laying can easily be estimated.
July 3, 1896.
HENRY C. MANCE,
M. Inst. C.E.
No. 3.
DEAR SIR,
F. E. HESSE, Esq., to MR. MERCER.
The Eastern Extension Australasia and China
Telegraph Company, Limited, Winchester House, 50, Old Broad Street,
London, EC. November 27, 1896.
As arranged, I send you herewith, for the information of the Committee, two statements, one giving particulars of the cable interruptions between Madras and Australia during the last five years, and the other showing the apportionment of the Australasian traffic for 1895 between Great Britain, the other European countries, and America.
I am, &c.
F. E. HESSE