702 THE COLLIERY GUARDIAN April 5, 1918. ELECTRIC CONTROL OF A DRAGLINE EXCAVATOR.* By L. W. Nickel. One of the most interesting applications of electric control in a field where reliability is essential can be found in the control of a dragline excavator. A machine controlled in this manner has recently been installed at the works of the Locust Mountain Coal Company, Shenandoah, Penn., for stripping a coa] bed, the stripping being from 14 to 30 ft. in depth. The rock encountered in the stripping process is drilled by steam drills and then shot. With the dragline in one position it is possible to take a cut 150 ft. in width. Spoil banks are always dropped on surface which does not contain coal; that is, the excavator is always placed directly over the vein and is followed by a steam or electric shovel. The drag- line method of stripping has been found to be much cleaner than any other, as no rock or dirt is spilled on the coal when once it is cleaned. This is not the case where it is necessary to run locomotive track for disposing of rock and dirt taken off the surface. With an electrically operated dragline no fireman, coal passer or pipe man is needed. Further, there are no steam or water pipes to freeze, and on the coldest mornings no delay is experienced in starting the stripping operation, it merely being necessary to close the main-line switch and commence work. The only labour required for the operation of this machine is the dragline operator, an oiler and a few men in the pit; whereas where stripping is being done by means of steam shovels and the dirt and rock are hauled away by locomotives, the amount of labour required is increased six or seven times. The dragline excavator under discussion has a turntable 24 ft. in diameter, a 150 horse-power hoist motor, and a 75 horse-power swing motor. The turn- table consists of 40 open-hearth steel rollers revolving between two 90 lb. rail circles, 24 ft. in diameter, one attached to the bottom of the revolving frame and one to the top of the base. The main machinery is driven by a 150 horse- power, 440 volt, slip-ring type motor, operating at a speed of 565 revolutions per minute. This motor drives two drums, one of which winds the rope that drags the bucket through the dirt while the other operates the rope by means of which the bucket is hoisted. There is also a small drum for raising and lowering the boom. the maximum speed position and to reverse at full speed. The current inrush during this plugging period operates the series relay having control of the plugging switch, and in this way resistance is cut into the rotor circuit of the swing motor, so that the motor is fully protected during the plugging period. Because of the momentum of the boom on an equipment of this kind it is not necessary, under ordinary conditions, to reverse at full speed ahead, inasmuch as the operator often throws the controller to central position at approximately 20 degs. ahead of the dumping pile, the momentum carrying the boom to this point, at which time the motor is plugged. The grid resistance for the motors is mounted at the rear of the control boards in open frames thoroughly protected and ventilated. The power for this installation is furnished by the Harwood Electric Company’s plant at Hazleton, Penn., 22 miles distant. It is transmitted at 25,000 volts to Shenandoah, where it is stepped down to 4,000 volts, and is again stepped down to 440 volts by the Locust Mountain Coal Company at its strip- pings, so that when brought to the dragline system it is three-phase, 440 volt, 60 cycle current. The transformers are mounted on a wagon. The current is commutated to the machine by means of a collector-ring equipment consisting of three copper rings mounted concentric with the centre casting of the machine and revolving with it. Heavy brass brushes to which the cable is attached are anchored on to the machine, there being two brushes for each phase. This makes a total of six brushes for the three rings, the brushes being mounted 180 degs. apart. THE VARIATION OF THE MAGNETIC COMPASS FROM THE TRUE NORTH. We have received the following communication from the Meteorological Office: Accuracy in underground surveying depends largely upon the precision with which the magnetic declination —that is to say, the variation of the direction of the magnetic compass from true north—is known. The declination is not only different in different places but it is subject to variations from week to week, from day to day, and even from hour to hour. Sometimes the BOOK NOTICES. The Economic Geology of the Central Coal Field of Scot- land: Description of Area II. By L. W. Hinxman, C. B. Crampton, E. M. Anderson, and M. Macgregor. 9f in. x 6 in. pp. 92. 77 figs, and ix. plates. Pub- lished by the Director-General, Ordnance Survey, Southampton. Price 4s. 6d. net. This memoir is the third of the series, now in course of preparation by the Geological Survey of Scotland, describing the economic geology of the several areas of the Central coal field. The district described in the present volume extends from Cumbernauld and Plean in the west, to the River Avon and the shores of the Firth of Forth, north of Grangemouth, and includes the coals and ironstones of the limestone coal group in the Plean and Denny area, and the coal measure coal fields of Banknock, Carron, Falkirk, and Slamannan. The valuable fireclays and ganisters of Cumbernauld, .Castle- cary, and Bonnybridge are also referred to in detail, with the results of analyses and physical tests of the clays from different horizons. Reference is also made to the lime- stones, igneous rocks, and superficial deposits where these are of economic value. Horizontal and vertical sections showing the structure and stratigraphical sequence in different parts of the area are appended. The Mining Manual and Mining Year Book, 1918. By Walter R. Skinner. 8£ in. x 5 in. pp. 936. London : W. R. Skinner and the Financial Times. Price 17s. 6d. net. The 1918 volume of the Mining Manual and Mining Year Book is the thirty-second consecutive annual issue since the publication of the first one in 1887. All those interested in mining enterprise who have reason to study the financial position of individual companies, or to obtain light on their potentialities either now or in the trade war which will doubtless follow the military one, will find the present volume indispensable. The work covers every section of the mining market, and many mines whose shares are not dealt in at present on the London Stock Exchange are included. In a world-wide industry, such as is mining, the progress of evolution is continuous and varied, and therefore to embody every new phase requires unremitting effort and endless expenditure of time, both of which have been employed without stint. The strict alphabetical arrangement followed as regards the body of the work has been found the handiest form for quick reference. For list purposes and cross-references— especially to those not very familiar with Stock Exchange nomenclature—the exhaustive index will be found a very helpful feature. The supplementary index contains the names of those companies which, although still in existence, have either ceased to be of public interest or are in too dormant a state to justify their inclusion in Mean Magnetic Declination at Kew, in Degrees and Minutes, for each Two-hour Interval in the Week March 24 to 30, 1918. Magnetic character. Intervals—Hours G.M.T. 0h.-2h. 14° + 1 2h.-4h. 14° + 4h.-6h. 14° + | 6h.-8h. 14° + 8h.- 14 -10h. ’+ 10h.-12h. 14° + i 12h.-14h. 14° + 14h.-16h. 14° + 1 16h.-18h. I 14°+ i | 18h.-20h. ; 14°+ 20h.-22h. 14° + I 22h.-24h. 1 14° + I Mean for day. 1 14° + i Min. Min. Min. • Min. ! Min. Min. Min. Min. Min. Min. Min. Min. Min. Sun., March 24 0 52’5 53'5 53'0 | 50'5 i 49'5 54'5 59'5 58'0 54'5 53'0 52'5 53'0 i 53'5 Mon., ,, 25 0 53*5 53'5 52'5 1 50'0 48'5 55'0 59'5 57'5 53'5 52'0 50'5 52'5 ! 53'0 Tues., ,, 26 0 53-5 53'0 51'5 48'5 49'5 58'5 62'5 60'5 57'5 54'5 53'0 i 51'5 : 54'5 Wed., „ 27 1 52'5 53'0 51'0 49'0 48'5 57'5 64'5 64'0 57'0 51'0 48'5 51'0 : 54'0 Thurs., „ 28 0 51'0 51'0 50'5 50'0 49'0 55'5 62'5 61'0 57'0 54'5 52'5 51'5 54'0 Friday, „ 29 1 52'0 i 51'0 49'5 49'5 50'0 56'0 60'5 57'5 53'5 52'5 52'5 50'5 53'0 Sat., ,, 30 1 52'0 53'0 53'0 49.'5 49'0 i 55'0 60'0 57'5 i 53'0 50'5 1 50'5 52'5 53'0 Diurnal inequality March 1917 (i.e., 1 lh. 2h. 3h. 4h. 5h. 6h. 7h. 8h. 9h. lOh. llh. 12h. 13h. 14h. 15h. 16h. 17h. 18h. 19h. 20h. 21h. 22h. 23h. 24h. departure from mean value for day) S 1 J -11 -1-2 -1-1 -i-o -1-2 -1'6 -3'2 -4'7 -4'7 —2’7 + 0’8 +4’3 + 60 +5'9 + 4'4 +2'8 i + 1'5 +0'4 + 0'1 -0'3 -0'5 -0'6 -1'0 -1'2 Mean value for March 1917 15° lz'9 The day is counted from Oh. (midnight) to 2 th. (midnight) G.M.T. Character e< 0” means a day wholly free from any but small disturbances. Character 1 means a day part or all of which is moderately or considerably disturbed. Character “2” means a day p^rt or all of which is highly disturbed. The normal value for an hour is the mean declination for that hour in the month, derived from quiet days only, or from all days excluding those of character “2.” On a day of character “ 0 ” declination at any hour will usually be within about 3' of the normal. On a day of character “ 1 ” the departure from the normal will usually not exceed 5', but it may occasionally be as much as 10', or even more. On a day of character “ 2” the departure from the normal will seldom exceed 20', but departures of 30' or even on extreme occasions of 1° or more may occur. The above values are obtained from measurements made after “ smoothing ” the curve. The swinging machinery is operated by a 75 horse- power, 440 volt, slip-ring type motor, driving a vertical swinging shaft through three gear reduc- tions. A pinion on the vertical shaft engages the circular swinging rack on the base. The master con- trollers, brake levers, etc., are mounted at the front of the machine so that the operator can manipulate the excavator without danger to the pitmen. The bucket has a capacity of 3| cu. yds. and is suspended by a three-part hoist. It is dumped by locking or holding the third, or single, part of the hoisting line. This is attached to the front end, or arch, of the bucket, after which continued hoisting dumps the contents. The brake, or holding device, consists of a drum, with a spring-actuated pawl and ratchet located near the front of the boom and con- trolled from the operator’s platform on the revolving frame. The magnetic control panel for this equipment was furnished by the Cutler-Hammer Manufacturing Company, of Milwaukee, Wis. It consists of double- pole magnetically operated switches equipped with series relays. The master drums, which are mounted over the operator’s head, are of the bevel-gear type equipped with punched brass fingers having a forged copper tip so designed as to prevent stubbing of the finger. The main motor controller is equipped with jamming relays so operated that the resistance is automatically cut into the rotor circuit when the motor is stalled. The maximum current taken by the motor under these conditions will not cause the circuit breakers to open. Thus the operator has control over the motor while it is stalled. This feature of stalling the motor and providing absolute protection makes it possible to obtain digging characteristics similar to those of a steam-actuated machine. The controller for operating the swing motor is equipped with a plugging switch so that it is possible for the operator to throw the controller quickly to * Coal Age. fluctuations in what are called magnetic storms, lasting for some hours, which in the last few months have been very noteworthy, are such as to make accurate surveying impracticable. Regular records of the magnetic declination are obtained in this country at the Royal Observatory, Greenwich; at the Observatory of the Society of Jesus, at Stonyhurst; at Richmond, Surrey, the Central Observatory of the Meteorological Office, known as Kew Observatory ; and at Eskdalemuir, Dumfriesshire, where a magnetic observatory was placed ten years ago, out of reach of present disturbance by electric railways, and it is hoped of future disturbance also. These observa- tories all have automatic records of the changes in the variation of the compass in their own locality, and as the variations are, generally speaking, world-wide and only slightly different in amount at all the observatories in this country, the variations recorded at any one of them are of direct use to mine surveyors. The Meteorological Office, with which rests the administration of the observatories at Richmond and Eskdalemuir, Iris been conferring with the representa- tives of the Institution of Mining Engineers as to the best form in which this useful information might be published for the information of mining surveyors. At a meeting at the Office, at which were present, besides the director (Sir Napier Shaw), Lieut.-Col. H. G. Lyons, R.E., chairman of the Gassiot Committee, an advisory committee of the Royal Society in respect of the observatories; Dr. Charles Chree, F.R.S., in charge of the Observatory at Richmond; Prof. O’Shea, hon. secretary of the Institution of Mining Engineers; Prof. Louis, of Armstrong College, Newcastle-on-Tyne ; and Mr. George Spencer, of the Mapperley Collieries, a form of information, to be sent out week by week, was agreed upon. The Office undertook to supply the particulars to the institution and to the principal mining journals. The information for the week ending March 30 is given in the accompanying table. Similar details will be sent from the observatory each week. the body of the work. By turning to that one of the previous volumes set opposite the respective names of such companies sufficient information for most practical purposes can be obtained. No important innovations have been made in the body of the work. The practice of placing full tabular statements of the crushing results of all the various mining fields together at the beginning of the book has again been followed, as this system has proved the most convenient for ready reference and com- parisons. Alphabetical lists of mining directors, secre- taries, engineers and mine managers, with their addresses and the names of the companies with which they are connected, are as usual appended to the book. These lists are supplemented by an up-to-date dictionary of mining terms, revised in order to include the fresh puzzles set mining operators by the extension of enterprise to new fields, where unfamiliar currency, weights, etc., are employed. An appendix contains the latest registrations of new companies and other particulars, completing the information in the body of the work to within a few days of publication. Messrs. Fredk. E. Potter Limited, advertising agents and contractors, have transferred all business from Pen Corner House and Windsor House, Kingsway, to Temple Chambers, Temple-avenue, London, E.C. Shipments to Italy.—The control of all shipments to Italy has been centralised in the Italian Government Commission, Empire House, Kingsway, London, and all persons having consignments ready for shipment are requested to send full particulars to the Shipping Depart- ment (Mediterranean) of the Italian Government Commis- sion at the above address. Applications should include the following particulars:—(1) No. of C.I.R. Sanction, or W.T.D. Licence, if any. (2) Particulars of goods. (3) Weight and measurement. (4) Any circumstances which make special consideration advisable. On receipt of these particulars endeavours will be made to provide space, and, should this be found possible, the necessary instruc- tions will be given for shipment.