From introduction: "In this paper are assembled and summarized many subjects relating to the copper industry in North America. Production of mines and districts, history of the industry in North America. Production of mines and districts, history of the industry, geology, of the principal deposits, and mining methods and costs are discussed."

From introduction: "The purpose of this bulletin is to discuss the theory of crushing and grinding in relation to present-day discoveries and developments and to consider the various mechanical appliances from a theoretical basis."

From Introduction: "This paper is divided into four sections concerned with coal tar and light oils produced by high- and low-temperature carbonization."

From Introduction: "The present paper discusses regional resources, chiefly of gold, the existence of which has long been demonstrated by substantial production but which are so nearly marginal in value that their mining has been protracted and will probably continue indefinitely for many decades."

Report published by the U.S. Bureau of Mines which is a compilation of accidents in quarries located in the United States with data regarding the number and kinds of accidents as well as information about the mining operations (e.g., number of men employed, kinds of quarries, amount of work performed, etc.).

From Scope of Report: "In connection with the study of the oil-shale resources of the United States, the Bureau of Mines has carried on not only extensive laboratory and field investigations but has constructed and operated an experimental shale-oil plant in Colorado. This report is based entirely upon subject matter that appeared in published and unpublished manuscripts of the Bureau of Mines."

Report compiled by the U.S. Bureau of Mines including statistics on fatal and non-fatal accidents in coal mines located in the United States as well as data regarding the various operations (e.g., number of miners employed and average production). The information is organized into tables for comparison and the text draws some overall conclusions in the summary.

Report issued by the U.S. Bureau of Mines covering accidents that happened in metal mines located in the United States including statistics for injuries, fatalities, kinds and causes of accidents, and operational data, such as number of mine workers and shifts worked.

From Introduction: "The composition and carbonizing properties of 33 coals previously tested have been given in technical papers of the Bureau of Mines and in short reports published for the most part in the Proceedings of the American Gas Association. A complete list of publications on the work previous to 1937 is appended to this report. The present report gives the composition and carbonizing properties of seven additional coals from West Virginia. The data include results of blending test in which Beckley bed low-volatile coal was used with all the high-volatile coals except the Alma coal, with which Pocahontas No. 4 coal was used."

Report discussing earthquake activity in the United States during 1938. The report is broken down by regions and has sections for specific earthquakes.

Circular describing organization, equipment, and materials, and procedure in fighting, sealing, and unsealing mine fires and in recovery operations at the time of or after fires or explosions.

Tests on a high-speed single-cylinder engine are described. The regularity of the spark timing was varied by driving the timer from different engine shafts. A simple and reasonably accurate method of determining the spark timing is described. The results show that irregular spark timing may cause large errors in tests of the knocking properties of fuels. For the engine tested, it was found that a change of one crankshaft degree in spark restart was equivalent to an 0.85 inch Hg change in allowable inlet pressure.

"Tables of stiffness and carry-over factor are presented for members in which the cross section and axial load do not vary along the length of the member. These tables are of use in solving problems in the stability of structural members under axial load as well as in application of the Cross method of moment distribution when the effects of axial load in the members are considered. The interval between successive values of the argument is small enough to make interpolation unnecessary in engineering calculations" (p. 1).

Four models of outboard floats (N.A.C.A. models 51-A, 51-B, 51-C, and 51-D) were tested in the N.A.C.A. tank to determine their hydrodynamic characteristics and in the 20-foot wind tunnel to determine their aerodynamic drag. The results of the tests, together with comparisons of them, are presented in the form of charts. From the comparisons, the order of merit of the models is estimated for each factor considered. The best compromise between the various factors seems to be given by model 51-D. This model is the only one in the series with a transverse step.

Flight tests were made to demonstrate the particularity of employing fixed tabs in conjunction with a suitably designed differential linkage to reduce the force required to operate ailerons. The tests showed the system to be practicable with tabs of the inset type. The relative ineffectiveness of attached tabs for changing the aileron floating angle rendered them unsuitable. Experience gained in the investigation has indicated that the use of the system is limited to maximum deflections of one aileron relative to the other of less than 30 degrees and that the differential linkage should always be designed on the basis of the highest probable floating angle.

"The increase in the frictional resistance of a surface caused by the presence of rivet heads was determined by towing four planing surfaces of the same dimensions. One surface was smooth and represented a surface without rivet heads or one with perfectly flush countersunk rivets. The other three surfaces were each fitted with the same number of full-size rivet heads but of a different type arranged in the same pattern on each surface" (p. 1).

The effect on cooling of baffle length with optimum cylinder finning is discussed. Results from tests of several streamlined cylinders are given. It is shown that by employing several baffles the cooling can be increased several times.

"Tests were made of the Clark Y wing having split flaps with a gap between the flap and the lower surface of the wing. Lift, drag, and pitching moments were measured for the wing with three different sizes of flap. It was found that any gap between the flap and the wing reduced the lift, the drag, and the pitching moments, but that the center-of-pressure movement and the ratio of lift to drag were little affected" (p. 1).

"An investigation was conducted in the NACA 20-foot wind tunnel of the ramming effect of three general types of carburetor intake rams for radial engines, namely, the internal constant area type, the external constant area type, and the external expanding type. The rams were installed on a radial air- cooled engine nacelle, and tests were made with and without the propeller operating. The results indicated that the external types having entrances near the front of the engine cowling gave the greatest ramming effect" (p. 1).

"Preliminary fatigue tests on two aluminum-alloy wing-beam specimens subjected to reversed axial loading are described. The motion used consists in incorporating one or two reciprocating motors in a resonance system of which the specimen is the spring element. A description is given of the reciprocating motors, and of the method of assembling and adjusting the vibrating system" (p. 1).

An investigation was made to determine the aerodynamic properties of rectangular and tapered NACA 23012 wings with plain ailerons and a full-span split flap, the flap retracting ahead of the ailerons. Measurements were made of lift and drag and of pitching, rolling, yawing, and hinge moments for all conditions of full-span flaps neutral and deflected at different chord locations. The results of the tests showed that a 0.20c(sub w) full span split flap located at approximately the 0.75c(sub w) point gave higher lift coefficients than had previously been obtained with a conventional 0.20c(sub w) partial-span split flap of a length to permit satisfactory control with plain ailerons. Still higher lifts were obtained if the full-span flap, when deflected, was moved back to the aileron axis. Moving the flap back to the aileron, in general, improved the aileron characteristics over those with the flap retracted. The most promising arrangement of full-span split flap and plain aileron combination tested, both for high lift and lateral control, was the rectangular wing with 0.20c(sub w) deflected 60 degrees at the 0.90c(sub w) location with 0.10c(sub w) semispan ailerons.

"A flight investigation was made of the increase in effectiveness of ailerons that can be obtained by preventing flow of air through the wing at the hinges and of the possibility of reducing the aileron operating force by replacing ailerons having normal open hinge gaps with narrower but equally effective ailerons having sealed hinge gaps. Tests were made with a Fairchild 22 airplane with two sizes of plain unbalanced ailerons, one set having a chord equal to 0.18c, and the other chord equal to 0.09c. The results of the investigation show that improvement of the lateral-control effectiveness is obtained by completely preventing the flow of air through the wing at the hinge axis of conventional ailerons" (p. 1).

The gyroscopic instruments commonly used in instrument flying in the United States are the turn indicator, the directional gyro, the gyromagnetic compass, the gyroscopic horizon, and the automatic pilot. These instruments are described. Performance data and the method of testing in the laboratory are given for the turn indicator, the directional gyro, and the gyroscopic horizon. Apparatus for driving the instruments is discussed.

An investigation was made to determine the aerodynamic characteristics of tapered and rectangular wings with partial-span plain flaps. Two Clark Y airfoils equipped with center section and with tip-section flaps were tested. The results showed that the aerodynamic characteristics of partial-span plain flaps were, in general, similar to those of split flaps of the same span, but that the lift and the drag were less for the wing with plain flaps than for the wing with split flaps of comparable size. For the rectangular wing with center-section plain flaps, the maximum lift and the lift-drag ratio at maximum lift were greater and the drag at maximum lift was less than for the wing with tip-section plain flaps of the same size. The maximum lift of the tapered wing varied in the same manner as that of the rectangular wing but the drag and the lift-drag-ratio relationship were opposite.