Owing to th e relative incom pressibility of w ater m odern high explosives can sink ships a t quite a distance, a fact exploited in the acoustic mine developed by th e G erm ans in the recent war. These mines were laid from planes, subm arines, and small surface craft and called for a new ty p e of “ sweeping ” operation based on th e use of sound. Luckily for us two mines were placed in shoal w ater and safely dism antled. The m echanism which caused the propeller beats of passing vessels to close a relay circuit and fire the mine was thus m ade available for expert scrutiny. The receivers of these acoustic mines had been tu n ed to respond to a sound wave common to m ost propeller-driven ships and once this was established we were able to develop a resonating device which pro
duced th e same effect b u t broadcast it to a safe distance from th e mine-sweeper. The
“ ham m er-box is a m etal drum containing a pneum atic ham m er and the vibrations can be directed and to some degree focused over a desired segm ent of th e sea. T hus a tool of the riveting-ham m er type, driven by compressed air, found a new job to do in th e war.
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A n aeroplane, norm ally a freighter, b u t capable of being equipped as a “ flying workshop ” has been developed here and should be of value in tim es of emergency on m ines lacking a n essential spare p a rt. The
floor supports a u n it load of 200 lb ./sq . ft., or a vehicle w ith a wheel loading u p to 5,000 lb., on a fairly flat surface. The door sills are only 4 \ ft. up, in the nose, and the freighter can use a short and poorly-kept runw ay.
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One use of th e cyclotron is to render radio-active th e atom s used in discovering w h at happens w hen chemicals are fed to vegetables. Such questions as the synthesis of chlorophyll, starch, and sugar from the in teraction of sun, w ater, and soil n u trien ts have trem endous p o ten tial value and these tem porarily radio-active atom s can be followed by use of the Geiger counter, which is sensitive enough to detect a single
“ tagged ” atom , and, luckily, this tagging does not a lter th e norm al chemical process.
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One w ay of cu ttin g down a big tree w ithout undue exertion is to apply a nichrom e wire m ade red h o t by an electric current.
This idea was used successfully b y an electrical engineer, who took off th e branches first and th en felled th e tru n k by sections.
The wire was atta c h e d in a semicircle, heated w ith low-voltage current and pulled through th e wood by weights. Small branches w ent quickly, b u t a 10-in. tru n k took all night.
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The bolting up of stru c tu ra l steel has been m ade a sim pler job b y th e developm ent of th e pneum atically-operated im pact wrench.
A fu rth er possibility for this tool is its use in ream ing out th e bolt-holes. To do this, one or tw o bolts of th e size being used on th e job are slipped on to th e shank of th e ream ing tool and welded there. The operator then has a pow er-operated tool in his k it which is im m ediately available if he has to deal w ith a misfit.
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In a recent lecture G. A. Maunsell to ld th e sto ry of préfabrication and em ergency construction of some of the A dm iralty re
inforced concrete stru ctu res which did such good w ar w ork.1 T he Sea F o rts which
1 Journ. R oy. Soc. A rts, M ay 10, 1946.
blossom ed suddenly in th e open sea and cylindrical towers. One im p o rta n t ingredient in th is rap id building was th e th in pre-cast cast flat in piles, w ith sheets of paper betw een them , in rapid-hardening cem ent, and after m echanical fittings proceeding sim ultane
ously. A dock took altogether some nine a pencil-m aking firm for pulverizing graphite.
I t is a sim ple long pipe th ro u g h w hich th e corrosion losses inevitable w ith electrolytic pickling baths. In it th e m etal is tip p ed into loosely-adherent m etal, w hich comes off when th e h eated m etal is rem oved an d dipped into
OCTOBER, 1946 235 prosperity and, despite neglected plantations and w ar-dam aged alluvial m achinery, a )ii of high-level flying, its m onotony, and fatigue
m ake it desirable th a t the business should be fighter really usher in single-wing service flying.
Power in an i.e. aero engine can be increased (fuel apart) in three w ays—by using bigger pistons, m ore cylinders, and supercharging. D etonation develops w ith a piston m ore th a n 6 in. in diam eter and supercharging has kindred lim itations, while e x tra cylinders m ean more weight and reciprocal-powered high-speed aeroplane has probably had its day. In May, 1941, the first W hittle jet engine took the air. As speed rises into the 500-600 m .p.h. zone the efficiency of the airscrew drops steeply and 600 is considered th e lim it to which a propeller-driven craft could fly.
As flying approaches the speed of sound the com pressibility of air raises difficulties, unstable shock-loading pressures developing.
Some advantages for high-speed work of jet- propulsion engines are th a t no elaborate valves are used and no m agnetos or spark
plugs. The engine is self-cooled and sm ooth- running, w ith sim pler problem s of bearing- design and lubrication. Many further advantages result from the absence of reciprocating and high-pressure parts. The turbine is far less “ fu ssy ” about its fuel or reciprocating engine. Since the avoidance
of deto n atio n effect is not a d om inant high and fast jet-propulsion gives running costs com parable w ith th e older m ethods. spotting, fog and navigation aids, gunlaying, and o th er applications. To send forth the folded. The excess m ate rial is either pounded off th e stacks of cu t card b o ard b y m en wielding m allets, or strip p ed aw ay by
OCTOBER, 1946 237 Nairobi, thence going through Tanganyika and th e Rhodesias to Johannesburg and on to Cape Town.