Search Documents

By D. W. Brunton

THE maps of our large mines are usually prepared with the greatest care; and it is somewhat singular that, in comparison with the great amount of time and money spent in surveying and platting, so little actual use is made of them. Almost the only purpose for which a completed survey-map is afterwards consulted, is the determination of the relative position of the different workings to each other, and to the boundary-lines of the property. After the completion of such a map, it should be made the beginning of another, and in most cases a far more important, undertaking, namely, its utilization as -a starting-point for a complete inventory of the company's underground possessions. The ordinary mine-survey map, being nothing but a record of what has been done, is, in one sense, only ancient history. To increase its value, such additions should be made as will render it a complete statement of the amount and value of ore in sight at any particular time, and a guide for future develop¬ments. Comparatively little extra labor is involved in this undertaking, since the larger and most expensive part of the work has already been completed when the mine has been surveyed and mapped. The necessary additions consist in working out, and platting on the maps, the geology of the mine as exposed in the workings, in such a manner that the geological survey may be of daily use in the development and operation of the mine. The first step towards the production of a geological map consists in tracing individual level-sheets from the general or composite map. The area to be included, outside of the property in question, will depend very much on local conditions; but, for geological, legal and commercial reasons, it should be extended as far as reasonably practicable. The scale to be

Sep 1, 1905

By E. D. Gardner

Introduction Oil shale deposits have been exploited in various countries throughout the world, but generally with government aid. The oil-shale industry of Scotland perhaps is the oldest and best-known; the largest was conducted in Manchuria by the Japanese during World war 11 as a source of liquid fuels for military uses. In general, foreign oil-shale deposits that have been exploited are much lower grade than those in the western United States. Considerable interest began to be shown in western oil shales in 1916; the peak of activities was in 1923. The catlin operation, near Elko, Nevada, perhaps was the nearest approach in this country to an oil-shale enterprise on a commercial scale. Over 100 companies were formed, ostensibly for exploiting the oil shale; a large number of them, however, proved to be stock promotions only, which gave the embryo industry a black eye. The Bureau of Mines operated an experi-mental oil-shale retort plant near Rifle, Colorado, from September 1926 to June 1927 and again from April 1928 to July 1929, after which the plant was dismantled. By this time the East Texas oil fields had come ill and the country lost interest in substitute liquid fuels. During World War II the Nation again became concerned about the magnitude of its petroleum reserves. Congress (April 1944) directed the Bureau of Mines to build and operate demonstration plants to produce synthetic liquid fuels from coal, oil shales, and agricultural and other products; a five-year Program was authorized. *' a part of this program the Bureau of Mines has built, at Anvil Points near Rifle, Colorado, a retort plant and develOped an experimental mine to supply the plant with oil shale. An important part of the mining work at Rifle is to devise methods and select practices for mining the oil shale on a commercial scale at the lowest practicable cost. The product to be mined has a relatively low value, a fact that must be kept in in mind. The combined aim of those in charge of the mining and those in charge of retorting is to demonstrate that the shale oil can be produced at a cost per barrel corresponding to the current quotation for crude petroleum —or at least very close to it. Plans call for an uninterrupted flow of broken oil shale from the lace in the mine, through crushers, through the retorts and thence to the disposal dump. The disposal of the spent shale in the Ride area should present no unusual problem. Mining research has consisted so far of Paper studies of the general phases of the probleml determination of the widest Span that the roof Stone will stand safely unsupported, and drilling problems. underground development has not proceeded far

Jan 1, 1949

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Jan 1, 1938

By Coolbaugh, Franklin

CRUSHING of Climax mine-run ore is carried out in two plants: No. 1 plant (flowsheet in Fig. 1) has a capacity of approximately 5000 tons per day. It is used as a stand-by except when maximum production is required. No. 2 plant (Fig. 2) has a top capacity of approximately 17,000 tons per day. The No. 2 crusher is more efficient to operate on reduced tonnages regardless of the wide variation in peak capacities. The system of crushing is similar in both plants: Mine ore, of a size which can be drawn through 48 by 96-in. slusher openings underground, is dumped into the crusher bins from ten-ton mine cars and fed into 48 by 60-in. Buchanan jaw crushers by means of chutes and Ross chain feeders. The jaw crushers are set to discharge at approximately 9-in. size. Jaw crusher discharge is conveyed to 7-ft. Symons standard cone crushers where it is broken to minus-2-in. size,

Jan 1, 1946

By R. S. Handy

THE properties of the Patiño Mines and Enterprises Consolidated, Inc., a New York corporation, are near Llallagua in the department of Chayanta in the west central part of Bolivia, South America, about 80 miles southeast of Oruro and 250 miles southeast of La Paz, the largest city in Bolivia and its virtual capital. The properties are accessible by railroad from three points on the west coast-from Mollendo, Peru, across Lake Titicaca, from Arica by way of La Paz, and from Antofagasta, Chile. The latter route, although the longest, is recommended by the companies as affording a more gradual introduction to the high altitudes; the mine being 13,000 ft. above sea level. The company operates its own railroad from its properties at Uncia to Machacamarca on the Chile & Bolivia R. R., a distance of 60 miles. This railroad is well equipped and well operated, and its location among the mountains surrounding Uncia represents excellent engineering skill. In fact all of the railroads, although they are of only a meter gage, are remarkable for the excellence of their construction, the arrangement of their dining and sleeping cars and the precision of their operation. There is only one drawback to rail- road and hotel accommodations and that is the absence of heating facilities, which does not seem to affect the natives but keeps a tenderfoot's teeth chattering continually. The company is a consolidation of the Patiño company, owning properties at Uncia, with the Compafiia Estanfera de Llallagua, a' Chilean corporation owning contiguous properties at Llallagua. Before the consolidation these companies were deadly enemies, and there still remain at the surface plant at Uncia the fortifications and underground defences provided during the warfare between the two factions. Also, in the Azul, or "Blue" tunnel at the junction line between the two properties is a strong steel barricade still bearing marks of the bullets fired during the various armed tilts between the workmen of the two companies. The headquarters for the mining operations and the milling plant have been moved since the consolidation from the original location at Uncia to the Llallagua side of the mountain, where the Chilean company's operations were carried on. The historic old town of Uncia, with its massive stone buildings of Spanish design, is a wreck, while the Llallagua side is being rapidly built up with modern structures.

Jan 1, 1929

By AIME AIME

THE petroleum engineers have the conference habit. They drop in, thresh things over, and drop out. No time is wasted. So it was at the Fort Worth meeting of the Petroleum Division, Thursday and Friday, Oct. 8 and 9; headquarters, Blackstone Hotel. Associate Chairman Albertson arrived the morning of the 7th, to tie in any loose ends of the technical program. S. M. Greenidge, chairman of the local committee, checked the arrangements with his committeemen at a luncheon that noon. By mid-afternoon the next day's attendance was anybody's guess-there were no noses to count. But when the gavel sounded Thursday morning 175 members and guests were present, also the official A.I.M.E. party consisting of President Lovejoy, Secretary Parsons, and George Otis Smith. Shortly after adjournment Friday afternoon all but a handful had vamoosed, lit out, disap¬peared. But, in the meantime, it was a grand conference, attendance maximum every session, and the discussion fast and furious. The discussion came from all over the floor, sometimes as good-natured sniping, sometimes in long volleys that were almost fatal to the reporter. Everyone knew his subject and few there were who had nothing to say.

Jan 1, 1936

By Frank L. Nason

(New York meeting, February, 1912) IN the year 1904 an eminent Swedish geologist prepared a report on the iron-ore reserves of the world. His estimates follow: Countries. Tons. United States, 1,100,000,000 Great Britain, . 1,000,000,000 Germany, 2,200, 000, 000 Spain, 500,000,000 Russia and Finland, 1,500,000,000 France, 1.500, 000, 000 Sweden, . 1,000,000,000 Austria-Hungary, . 1,000,000,000 Other countries, 1,200,000,000 Total, . 10,000, 000, 000 The iron-ore allotted to the United States by the Swedish geologist is barely sufficient to last 20 years at the present rate of consumption. On the other hand (according to Edwin C. Eckel,1 from whom the above and following statistics are quoted), there is hardly need for worry on the part of our iron industries for the, next two centuries or more. Upon the basis of careful work by the U. S. Geological Survey, in which Mr. Eckel has taken an important part, the following estimates arc definitely, but by no means finally, given for the United States District. Tons. Lake Superior District, . . 1,500,000,000 to 2,000,000,000 Alabama, red hematite. . . 1,000,000,000 brown hematite, 725,000,000 Georgia, red hematite, 200,000,000 brown hematite, 125,000,000 Tennessee red hematite, . 6110,000,000 I brown hematite, 225,000,000 Virginia., red hematite, 50,000,000 brown hematite, 300,000,000 Total, . . 4,725,000,000 to :5,225,000,000

Jul 1, 1912

By Arcy A., J. G. Davis, D&apos Shock

Results of a pilot operation in the Carlsbad Basin are discussed. After hydrafracing between wells, a block of potash was removed by solution techniques. The distance between frac wells was about 200 ft, the thickness of potash mineralization, 5 ft. By proper manipulation, a feed of concentrate brine was obtained. The ex-periment showed that the thin-bedded potash could be removed by the solution techniques. The details of well construction, method of operation, and removal rates are discussed. Continental Oil Co.'s laboratory research on the fundamentals of potash solution mining has been expanded by means of a series of field tests, and subjects such as well completion and hydraulic fracturing were added to the investigation. Both single-well and multi-well systems were studied in the field work. Discussion Background: The current paper discusses one field test in which potash was solution mined by a two-well system from a thin sylvinite zone. The potential economic value of solution mining evolves from (1) the use of drilled holes and solution techniques instead of excavated shafts and caverns and (2) the ability to mine both land and marine deposits through any type of overburden geology and below conventional mining depths. Recent interest has been focused on potash' and other soluble minerals, such as trona. Solution extraction minerals, such as copper and uranium, are also worthy of important consideration. In addition, many of the techniques are directly applicable to the construction of horizontal underground storage carverns in salt. There are two general approaches to potash solution mining. The first is to mine on a single-well basis, in which the same well bore is used for both injection and production. This method is slow, and the areal extent may be quite limited in other than very thick ore zones. The second, and the preferred approach, is to mine on a multi-well basis in which the solvent is circulated between wells. This technique, if applied in a manner which allows the ore zone to be mined from the bottom upward, results in nearly all the solution taking place from the cavern roof. Salt removal rates, therefore, are very much higher than from a single-well system.l Wells can be interconnected into a multi-well pattern by several means. One is to join single-well caverns in the lower part of an ore zone. Another is to use the hydraulic fracturing techniques developed in the oil fields.' We preferred the fracture approach because of its potential for creating the greatest area of salt exposure. Test Site Description: The field tests were conducted in New Mexico's Carlsbad Basin, where the potash deposits are flat and uniform over reasonable distances. Here, 12 potash zones are present in the massive Salado Salt section. The specific target was the Third Ore Zone which is about 4 ft thick at our location and about 1150 ft deep. The test pattern was designed in the shape of an equilateral triangle with a fourth well located in the center, 200 ft from each of the vertex wells. This configuration allowed the ore zone to be hydraulically fractured from the center well with good assurance that the fracture would intersect the bore of at least one outside well. Several multi-well test patterns would be available if the fracture connected all wells. Well Completion: Surface casing was set in the top of the Salado Salt at 600 ft to shut off water flows from the surface sands, and the salt section was drilled and diamond-cored to a point below the Third Ore Zone. A drilling fluid made of diesel oil with a small amount of emulsified water was used to drill and core the salt. This fluid was highly successful in preventing enlargement of the drilled hole and in promoting good core recovery. The three outside wells were completed by setting 51/2-in. casing at the base of a streak of anhydrite about 20 ft above the ore zone. Pipe was set high so that the intersection point of the fracture could be detected even if the fracture migrated above the ore zone as it progressed outward from the center well. The center well itself was completed by cementing 51/2-in. casing through the Third Ore Zone. Cement bond logs run on the center well have shown excellent bonding. Fracturing Practice: A mechanical tool was used to cut a notch through the casing and into the salt at a point about 1 ft below the ore zone in the center well. The purpose of this notch was to fix the point of fracture entry into the salt. The fracturing was done with water at injection rtaes as high as 30 bbl per min. The salt parted at 1450 psi; and it required only 5 min for the fracture to reach the well which was 200 ft to the south. It took about 5 min more to reach the other two wells. Caliper surveys were run to locate the point of fracture entry in the three outside wells. The fracture appears to have drifted downward slightly, entering the outside wells at the top of a streak of carnallite 8 or 9 ft below the ore zone. A cross section of the wells selected for the multi-well test is shown in Fig. 1. The figure includes KC1 values based on core analysis and the trace of the fracture plane between the wells.

Jan 1, 1971

By S. S. Hsieh, J. R. Lehr

Bench scale beneficiation studies were made on Idaho dolomitic phosphate rock using the TVA carbonate flotation process. The process used diphosphonic acid as a phosphate mineral depressant and fatty acid as a carbonate mineral collector. Silica was subsequently rejected as float using an amine collector, with phosphate product recovered as the sink fraction. Two samples of prepared flotation feed from commercial operation were used. One contained 21% P205 and 3.2% MgO. The other contained 26% P205 and 1.8% MgO. The results indicate that concentrates containing 31% to 33% P205 and 1% or less MgO can be obtained, with about 80% P205 recovery.

Jan 1, 1986

By Howard Willey

MINING operations of the Charcas unit at present are limited to the Tiro General mine at Charcas, in the State of San Luis Potosi, Mexico. The Tiro General mine was first operated during the Spanish occupation of Mexico for rich silver ores in an oxidized zone along the outcrop of the principal vein. In depth the ore is a complex sulfide with widely varying proportions of sphalerite, argentiferous galena and chalcopyrite; and until recent years, it was economically impossible to carry on mining otherwise than irregularly in sections of the veins richest in galena and chalcopyrite. The advent of selective flotation brought the orebody as a whole within the field of economic interest, and a flotation mill of 650 metric tons daily capacity was constructed in the year 1925. The mining of partly worked-out sections of the mine, as well as the very heavy ground in most of the stopes opened in virgin ore, presented an unusually difficult problem. This -paper describes the so-called "filled top slice" stoping method finally adopted as the standard system.

Jan 1, 1930

By AIME AIME

EITHER the 2300 people who came to the Annual Meeting were in a better frame of mind or they were resigned to their fate, or it was a better meeting than usual. Whatever the reason, at the 1nstitute?s 148th meeting the attendance was better than ever before, things went more smoothly than in some previous years, and complaints appear to have been almost entirely absent. Patience was sometimes reauired but. almost without exception, it was forthcorning the well-known recession seems to have given many members enough leisure time to come to the meeting without depriving them of the tangible wherewithal to come.

Jan 1, 1938

By A. C. Fieldner

COKE and by-products have prime importance in the war program. The past year was marked by the construction of new and the rehabilitation of old by-product and beehive ovens and by the increase of production from existing plants to practically 100 per cent capacity. W. T. Brown's paper, "Plan to Improve Blast-Furnace Coke," presented at the Fuels Conference in St. Louis, Sept. 30, showed how the blending of low- and high-volatile coal improved the physical properties of coke and that improvement of the quality and uniformity of coke favored an increase of blast-furnace capacity- a vital need in the war program. Others in the industry have likewise increased production of coke or recovery of by- products by various innovations or changes in operation. Recognition of the value of pooling these developments for the benefit of the entire industry led to organization of a survey of coke- oven plants and blast furnaces by the Bureau of Mines in co-operation with the Solid Fuels Co-ordinator with a view to improving metallurgical coke production and recovery of by-products. This survey is being conducted with the help of an advisory committee consisting of representatives of the Bureau of Mines, the Solid Fuels Co-ordinator, the War Production Board, and the blast-furnace, coke-oven, and coal-mining industries.

Jan 1, 1943

By H. LIVINGSTONE LMAN

A GOOD DEAL of information concerning flotation has come out during the patent litigation of recent years, and the legal situation has cleared considerably, to the satisfaction of Minerals Separation, Limited. Hence, Mr. H. Livingstone Sulman, one of the originators of the successful process of that company, felt at liberty to explain, on Thursday, Nov. 20, his experience and his views in a "Contribution to the Study of Flotation," before the Institution of Mining and Metallurgy. He did not give technical details. He dealt with the physical problems, so simple, as he remarked, that he had wanted 96 pages to express his views. He presented much data, partly new and based on observations of his own, bearing upon the very complex flotation phenomena in an instructive wav and made frequent references to the valuable researches especially of Prof. Edwin Edser and Mr. Emil Hatschek.

Jan 1, 1920

By K. Sassa, I. Ito

The dynamic principal stresses induced within rock by an explosion under con fined conditions are analyzed for the case of blasting with one free face by applying the values of measured radial displacement, particle velocity and so on to equations derived from the theory of elasticity. The dynamic stresses on the free face are also calculated from the strain measured by wire strain gauges affixed on the free face. Some results obtained are briefly: 1) The maximum stress on the free face appeared at the intersection between the free face and the burden, and its magnitude was about twice as large as the magnitude of the tangential tensile stress imparted by the incident stress wave within the range related to the breakage by blasting. 2) The maximum value of the compressive stress near the free face was decreased due to the existence of the free face, while that of the tensile stress was increased. 3) At any point near the free face, the directions of the principal stresses in the r? plane using spherical coordinates with the origin at the center of the spherical charge, changed with time except in the direction of the burden. However, at another point near the explosion point where the principal stresses were mainly those stresses caused by the initial longitudinal wave, the directions of the principal stresses coincided with those of the coordinate used. 4) The maximum value of the tensile stress in the F direction was larger than those in the re plane at and near the free face. 5) The tensile stress caused by the Hopkinson effect appeared only near the burden. 6) It is presumed from the results of stress analysis that radial cracks will be produced in the rock mass near an explosion point, but with the approach of the free face, the directions of cracks curve towards a direction parallel to the free face. INTRODUCTION In order to investigate the mechanism of rock breakage by blasting, it is considered to be very im- portant to know how the stresses are generated and distributed within the rock by explosion of a confined charge. As part of a research program concerning the mechanism of rock breakage by blasting, the authors have already published papers on the detonation pressure produced at the inner surface of the charge hole1 and on the behavior of the dynamic stresses within rock caused by an explosion in the case where no free face existed.' In this study the dynamic stresses on and near the free face have been investigated for the case of blasting with one free face. The mechanism of rock breakage in blasting is discussed in the light of these studies.

Jan 1, 1967

By W. R. Atkins

The Negaunee mine is at the east end of the Marquette Range, in the city of Negaunee, on the Upper Peninsula of Michigan. Iron ore was first discovered on this property in 1883 by diamond drilling. A shaft was sunk soon afterward. and the mine has been worked continuously ever since. The total shipments from 1887 to Jan. I, 1945, were 20,417,587 long tons. The mine was taken over by the present operators, The Cleveland-Cliffs Iron Co., in 1903. During the past four years, 1941 to 1944 inclusive, the property has produced an average of nearly a million tons a year, and has employed more than 400 men. Geology The ore body at the Negaunee mine lies in a large syncline dipping about 15° to the west, the ore coming to ledge at the east end of the trough. The ore occurs in the Negaunee formation of the middle Huronian age, which consists of ferruginous cherts and slates through which intrusions of diorite have occurred. Although these intrusions of diorite have an important bearing on the formation of ore on the range, they are not important in this ore body. Some faulting has taken place along the diorite intrusions, or dikes as they are called locally, and also other faults are known to exist across the formation. These faults do not complicate either mining or development of the ore body. The footwall consists of jasper underlain with Siamo slate; the hanging wall is jasper and ferruginous chert. Fig. I shows a typical cross section of the ore body. The ore body is quite regular, about 120 ft. thick in the middle of the syncline and thinning out toward both sides of the fold. Its width ranges from 400 to 800 ft., the average being about 600 ft. The footwall is uniform in dip and strike, but irregular lenses of ore often extend 50 to 75 ft. up into the overlying jasper capping. Method of Mining Ore in the Negaunee mine has been mined by top slicing almost exclusively since 1903 This method of mining has been employed because it is especially adapted to the size and shape of the Negaunee ore body, and to the soft, sticky nature of the ore as well as the generally soft, broken jasper capping. Development The ore body has been developed from six different levels with intervals varying between loo and 125 ft. On the average, the dip causes a horizontal offset of 350 ft. per level, and under these circumstances it has been necessary to carry on considerable development in rock to make available the ore lying along the north and east footwalls. This is not as disadvantageous as might be supposed, because of reduced pressure and the accompanying saving in maintenance costs. The development of the

Jan 1, 1949

By N. A. D. Parlee, E. M. Sacris

OVER 55 years ago, Sieverts and Hagenacker1 and Donnan and shaw2 made determinations of the solubility of oxygen in liquid silver, over a rather short range of temperatures (973° to 1125°C), using quartz bulbs, mainly at 1 atm. From the results of their investigations, Mizikar, Grace, and parlee3 plotted % O vs 1/T and obtained the following straight-line equation for solubility at 1 atm: log % O = 723.7/T - 1.0949 Recent work on the kinetics of the Ag-O2 system394 indicated there might have been some error due to reaction with the direct heated silica bulbs. Thus it became important to redetermine the solubility with the silver contained in a better refractory such as alumina, and by induction heating where the walls of the container were not so strongly heated. It was also desirable to extend the temperature range. A modified Sieverts apparatus of fairly standard type was used except that a special type of reaction tube was employed, Fig. 1. Dried argon with a guaranteed purity of 99.9 pet, and dried medical-grade oxygen with a guaranteed purity of 99.6 pet containing a little nitrogen, were the gases used. The measuring system consisted essentially of a manometer and a water-jacketed 100-cc gas buret with an open-end vertical tube parallel to the buret. This tube has the same diameter as the buret in order to give the same capillary effect on the mercury. A screw leveling device was used with the buret leveling bulb to help provide accurate pressure readings. A 2-mm ID capillary line connected the buret to the reaction chamber, helping to reduce the dead volume, which was determined with argon. The heating medium was a 2.5-kw output induction furnace. The induction coil was made of a 3/16-in. copper tubing with eight turns and an inside diameter of 4 cm. The reaction bulb was made of a quartz tube 18 cm long and 3 cm in inside diameter, Fig. 1. Inside the quartz tube were two alumina crucibles (Mor-ganite Triangle RR, XN10 and XN5) one inside the other. Below these two was an alumina disk. The disk prevented the corners of the outer crucible from expanding against the quartz tube. The solid sample (99.994 + pet Ag), which had been previously cleaned by air oxidation and repeated removal of scum, was placed inside the inner crucible. An alumina disk with a hole at the center covered the two crucibles. In order to decrease the dead volume, an evacuated quartz "filler" tube was placed on top of the crucible cover. The part of the reaction tube above the spherical joint was made up of Pyrex glass with a flat glass top. It was here that a prism was placed to facilitate the use of an optical pyrometer, previously calibrated at the freezing point of silver. This type of reaction bulb and furnace assembly was specially designed for this work, and used in preference to the relatively new water-

Jan 1, 1965

By W. A. Krivsky, R. Schuhmann

Jan 1, 1962

Nominating Committee.-On the recommendation of the President, the Board of Directors, at their meeting on Apr. 25,1913, appointed the following Nominating, Committee to nominate officers and directors for next year: John Hays Hammond (Ex-President), Chairman. Robert H. Richards Chairman of Boston Local Section. Richard S. McCaffery, . . . . Chairman of Spokane Local Section. Chester F. Lee Chairman of Puget Sound Local Section. Frederick G. Cottrell, . . . . San Francisco, Cal. Charles W. Goodale Butte, Mont. James W. Maleolmson, . . . . Kansas City, Mo.

Jan 5, 1913

By E. H. Rose

IN the realm of ore dressing the most pregnant feat of all time was announced in 1945: the winning of the mineral raw materials which made the harnessing of atomic energy possible. Lost in the stupendous implications of the end result, in the two billion dollar hugeness of the project, and in the famous names attached thereto, the fact that crude uranium ores had to be concentrated received relatively little notice in the press. Only the final link in the concentrating chain was publicized-ether extraction of uranyl nitrate, developed by Hoffman and carried on by the Mallinckrodt Chemical Works, or methods developed by the Ames group under Spedding. Some of the earlier links represented less glamorous but equally difficult and exacting research. One may only speak a word of admiration for those who worked hard, accomplished much, and said nothing. The universal lament for most of the year was "man shortage." A group of Canadian engineers expressed it as "being so short of labor that no labor was available to develop laborsaving devices." . Despite this, an outstanding amount of mineral-dressing progress was made in 1945. Necessity allowed no alternative. The insatiable demand of war for minerals forced the exploitation of lower and lower grade ores, and of others not before considered of commercial character or use, requiring the mineral dresser to fight for and win new bridgeheads on the home front.

Jan 1, 1946

By Donald Barton

THE theory of gravitation is based on Newton's law that any two bodies exert a mutual attraction which is proportional to the product of their masses and inversely proportional to the square of the distance between them; i. e., A =KRM/R2 (1) where K is a constant, M and m are the respective masses of the two bodies, and R the distance between them. In the earth's gravitational system, the earth is one of the bodies; the other may be any body within or without the earth. In theoretical dis¬cussions and calculations in regard to gravity, that other body usually is taken as a unit of mass: in the C. G. S. system, a body of one gram in mass. GRAVITY AND LEVEL SURFACES Gravity is defined in geophysics as the force of attraction exerted by the earth, towards itself, on a body of unit mass. The intensity of gravity is usually expressed in dynes of force or in centimeters of acceleration. In geophysical work in America, most commonly it is expressed in dynes (per gram) with the "per gram" understood and not directly expressed. In geophysical work in Europe, most commonly it is expressed in centimeters per second per second (cm./sec.2) and less commonly merely as centimeter-gram-second units (C. G. S.). At sea level, the intensity of gravity amounts very nearly to 980 dynes. The vertical is the direction along which the attraction of gravity is exerted at any point. . In most cases, it is very nearly, but not quite, per¬pendicular to the earth's surface. The path that would be taken by a body falling freely through space toward the earth is vertical at each point and may be spoken of also as "the vertical," or as the line of the vertical, or as a line of force of gravity. At the earth's surface it com¬monly is very nearly, but not quite, a straight line.

Jan 1, 1928