From Summary: "This is a report on a scale effect research which was made in the variable-density wind tunnel of the National Advisory Committee for Aeronautics at the request of the Army Air Service. While the present report is of a preliminary nature, the work has progressed far enough to show that the scale effect is almost entirely confined to the drag."

Report containing several articles discussing coal in the state of Virginia. These articles cover geographic deposition of coal, coal production, mining methods, and analyses of coal samples. Index begins on page 71.

Report includes the National Advisory Committee for Aeronautics letter of submittal to the president, congressional report, summaries of the committee's activities and research accomplished, bibliographies, and financial report.

Annual report submitted by the Boy Scouts of America to Congress describing highlights from 1924, activities, organizational leadership, and other information about scouting programs.

The Behm acoustic sounder for aircraft enables the barometric determination for the altitude by night or fog and therefore promises to prove of great importance in safeguarding air traffic.

From Introduction: "This report is divided into six parts as follows: (1) Occurrence of clays in Georgia and the source of the clays tested; (2) washing tests; (3) physical test; (4) utilization of kaolins white ware; (5) utilization of clays in refractories; and (6) utilization of clays in face brick."

Biennial report of the Board of Regents of the Texas State Teachers Colleges discussing activities of state teachers' colleges and providing an overview of relevant statistics and financial information related to state funding.

Technical paper issued by the Bureau of Mines over the Bowie-Gavin process. As stated in the introduction, "this paper describes a process and an apparatus designed to recover oil from such deposits" (p. 1). The results of experiments conducted using this process are discussed. This paper includes tables, illustrations, and photographs.

"We propose to show how to calculate the cooling capacity of all radiators through which the air flows in separate streamlets, whether enclosed in actual tubes or not and whatever cross-sectional shape the tubes may have. The first part will give the fundamental principles for calculating velocity of air in the tubes and the heat exchange by radiation, conduction and convection, and show, by examples, the agreement of the calculation with experiments. In the second part, the effect of the dimensions and conditions of operation on the heat exchange will be systematically investigated" (p. 1).

Technical paper issued by the Bureau of Mines over the development of carbon monoxide alarms and recorders. Descriptions of the recording equipment are presented and discussed. This paper includes tables, photographs, and illustrations.

This report, on the planing and get-away characteristics of the F-5-L, gives the results of the second of a series of take-off tests on three different seaplanes conducted by the National Advisory Committee for Aeronautics at the suggestion of the Bureau of Aeronautics, Navy Department. The single-float seaplane was the first tested and the twin-float seaplane is to be the third. The characteristics of the boat type were found to be similar to the single float, the main difference being the increased sluggishness and relatively larger planing resistance of the larger seaplane. At a water speed of 15 miles per hour the seaplane trims aft to about 12 degrees and remains in this angular position while plowing. At 2.25 miles per hour the planing stage is started and the planing angle is immediately lowered to about 10 degrees. As the velocity increases the longitudinal control becomes more effective but over control will produce instability. At the get-away the range of angle of attack is 19 degrees to 11 degrees with velocities from the stalling speed through about 25 per cent of the speed range.

Report compiled by the U.S. Bureau of Mines including statistics on fatalities 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.

From Summary: "The purpose of this investigation was to determine the performance, characteristics, and coefficients of full-sized air propellers in flight and to compare these results with those derived from wind-tunnel tests on reduced scale models of similar geometrical form. The full-scale equipment comprised five propellers in combination with a VE-7 airplane and Wright E-4 engine. This part of the work was carried out at the Langley Memorial Aeronautical Laboratory, between May 1 and August 24, 1924, and was under the immediate charge of Mr. Lesley."

"This report describes a roots type aircraft engine supercharger and presents the results of some tests made with it at the Langley Field Laboratories of the National Advisory Committee for Aeronautics. The supercharger used in these tests was constructed largely of aluminum, weighed 88 pounds and was arranged to be operated from the rear of a standard aircraft engine at a speed of 1 1/2 engine crankshaft speed. The rotors of the supercharger were cycloidal in form and were 11 inches long and 9 1/2 inches in diameter. The displacement of the supercharger was 0.51 cubic feet of air per revolution of the rotors" (p. 451).

From Introduction: "In view of the increasing importance of the diamond drill in prospecting for oil, the Bureau of Mines issues this bulletin."

Technical paper issued by the Bureau of Mines over studies on dust respirators. The development and efficiency of the respirators are discussed. This paper includes tables, illustrations, and photographs.

From Introduction: "Data collected by the Bureau of Mines indicate the United States a large percentage of the blasting in quarries, shafts, and tunnels, and from 15 to 25 percent of the blasts in mining operations, are set off electrically. The Bureau of Mines is interested in electric shot-firing because of its use in mining, and especially because electric methods, when properly applied, are undoubtedly safer than other methods commonly used."

Technical paper issued by the Bureau of Mines over testing conducted on lubricating oils on internal-combustion engines. Results of the tests conducted are presented. This paper includes tables, photographs, and illustrations.

"From theoretical considerations one would expect an increase in power and thermal efficiency to result from increasing the compression ratio of an internal combustion engine. In reality it is upon the expansion ratio that the power and thermal efficiency depend, but since in conventional engines this is equal to the compression ratio, it is generally understood that a change in one ratio is accompanied by an equal change in the other. Tests over a wide range of compression ratios (extending to ratios as high as 14.1) have shown that ordinarily an increase in power and thermal efficiency is obtained as expected provided serious detonation or preignition does not result from the increase in ratio" (p. 483).

"The work covered by this report was undertaken in connection with a general investigation of fuel injection engine principles as applied to engines for aircraft propulsion, the specific purpose being to obtain information on the coefficient of discharge of small round orifices suitable for use as fuel injection nozzles. Values for the coefficient were determined for the more important conditions of engine service such as discharge under pressures up to 8,000 pounds per square inch, at temperatures between 80 degrees and 180 degrees F And into air compressed to pressures up to 1,000 pounds per square inch. The results show that the coefficient ranges between 0.62 and 0.88 for the different test conditions between 1,000 and 8,000 pounds per square inch hydraulic pressure" (p. 371).

"With the assistance and cooperation of the National Advisory Committee for Aeronautics the Bureau of Standards has been engaged for the past year in an investigation of turbulence in wind tunnels, especially in so far as turbulence affects the results of measurements in different wind tunnels. Two methods of making such studies are described in this report together with the results of the use in the 54-inch wind tunnel of the Bureau of Standards. The first method consists in measuring the drag of circular cylinders; the second in measuring the static pressure at some fixed point. Both methods show that the flow is not entirely free from irregularities" (p. 465).

Report issued by the Bureau of Mines over investigations conducted on lignite. Preparation methods and uses of lignite are discussed. This report includes tables, maps, illustrations, and photographs.

Report issued by the Bureau of Mines over investigations conducted on lignite. Preparation methods and uses of lignite are discussed. This report includes tables, maps, illustrations, and photographs.

Report issued by the Bureau of Mines over studies conducted on red iron-ore mining near Birmingham, Alabama. Results of the studies are presented and discussed, as are mining methods. This report includes tables, illustrations, and photographs.