detnolishing concrete is mot-e expensive than explosives, it was found tha2t the ability to break blocks of -7 to IO tons for loading into trucks or railroad cars often means a saving in final cost as well as greater speed in completing the work.

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X-Raying for Safety.--(Safe/~ Engitzeering, Vol. 73, No. 3.) Modern industrial safety engineertng is vitally concerned in prevent- ing injuries that may take many years to incapacitate the workman and somc‘times take a long time even to make their presence mani- fest to the workman. The doctor now has a tool of his own to detect the oncoming trouble before it reaches serious proportions. This is the s-ray machine. I’reviously the cost of such a machine for this use has been a very important item. Now there seems to be a method and a medium which offers a solution of the cost problem particularly in chest radiographs. This recent development is receiving wide recognition and being applied to large groups of individuals for the purpose of screening out cases requiring attention or further examination. The method uses paper film in rolls and comprises a series of coordinated procedures and processes which so speeds up the marking, making, processing, reading and recording of diagnoses, that a thousand or more chest radiographs may be tnadc in an 8 hour day.

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Strength of Materials.-_A Special Summer Program and Con- ferences on Strength of Materials will be held at the Massachusetts Institute of Technology for four weeks beginning June 21, 1937.

There will be lectures on creep, fatigue of metals, and strength of materials by prominent men in these fields including the staff of the Institute. Laboratory exercises will be given in the testing of metals, making use of the more modern measuring instruments and apparatus. Four Seminars will be held during the course, to afford opportunity for the presentation of recent developments in allied fields of engineering mechanics.

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Radio Device Locates Underground Pipe Lines.-(A mericun Gas Journal, Vol. 146, No. 4.) A new instrument known as the M-Scope, an invention of Dr. Gerhart R. Fisher, Ilirector of the Fisher Kesearch Laboratories, is now being used successfullv for locating and mapping gas distribution lines. It consists esseniially of t\\-o specially designed radio units-a transmitter and receiver- the former sending out a continuous buzzing signal. \\‘hrn there is

132 CURRENT TOPICS. [J. I:. I.

no metal interposed between the units, a definite volume of sound is heard in the earphones of the receiver where a meter also gives a definite reading. If a metal object, even deeply buried, lies between the units, the volume of the signal increases and the meter reading becomes higher. In using the M-Scope for tracing an underground pipe line, the transmitter is set on the ground directly above it, and the operator, carrying the receiver, follows the path along which sustained signals are received. Sudden increases in the signals mean additional metal-a valve, junction, etc., just below. Sudden decreases mean that the line has turned aside or ended. Energy for both units is supplied by standard dry cells which last several months in normal service. Individual units weigh about 8 lbs. each.

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New Transatlantic Antennas.-Recently, engineers of the huge RCA international radio communications station at Riverhead, Long Island, set a number of 130 foot wooden poles for the support of new antennas. The rigging crew of the station towed the enormous sticks to position, up-ended them with gin poles and lowered them into concrete sockets in the ground with amazing speed. The poles are believed to be the largest one-piece masts in the East, with an average length of 130 feet and an average weight of four tons. They are of Douglas fir from the state of Washington. The new antennas, when completed, will have an increased average height of 60 to 70 per cent. over those previously employed, which is expected to result in more efficient operation in the longer part of the so-called short wave band of radio wave-lengths.

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If Lumber Warps, Maybe It’s “ Compression Wood.“-Anyone who handles lumber from coniferous trees is familiar with boards that bow, twist, and warp. The cause may be compression wood in the board, says a bulletin just issued by the Forrest Products Laboratory of the U. S. Dept. of Agriculture at Madison, \Vis. Compression wood troubles usually develop in lumber from the lower side of a large branch or lower side of a leaning tree trunk. Pressure from the weight of the branch or the top of the leaning tree deforms the individual cells. LVhen the lumber is sawed and the pressure removed, these abnormal cells begin to misbehave with every change in moisture. The wood fibers on opposite sides of a board do not shrink and swell in the same way and in the same proportion. Such lumber b en s and twists and pulls out of d. shape. Compression wood is low in strength for its weight and