The use of the aeroplane in reconnaissance has greatly increased the importance of eamon. fage, and the development of the camera has increased its difficulty. Camouflage was evolved by living organisms before man appeared. Its principles were first studied by feld zoologists and recommended by them to soldiers. These first studies were naturally concerned with how objects appear to the eyes and other sense organs of animals and men. But the image recorded by camera is not the same as that seen by a man. For instance, a building may be painted so that it is inconspicuous to the human eye. But when it is photographed by ordinary light or infra-red rays it may show up conspicuously. Paints which deceive the camera as well as the human eye are now needed, and their discovery requires the work of the chemist and physicist Tu the new edition of "Science in War" attention is drawn especially to the psychology of recognition. Everyone will have noticed how they have failed to find a large shop because some object by which they had been unconsciously recognising it had been removed. The changing of these labelling features on military Objects might with a little trouble greatly confuse the enemy. But more research is need-determine their nature.
'Motorists and, airmen desire engines that give the' maximum power for a given weight. They have gener&lly used four.stroke engines because the devotion of separate-strokes to the inlet, compression, expansion, and exhaust was the only method that had been found to ensure that each of these operations was done eficiently at high engine speeds. It is evident that if a two-stroke cycle could be used efficiently there would be a big increase in power for a given weight, because each cylinder would then have twice as many working strokes and deliver -twice as much power.
The running of the two-stroke engine at high speeds has, however, proved difficult owing to the inefficiency of the known methods of charging and exhausting the cylinders. A discovery by the Polish inventor M. Kadenacy promises that this difficulty may be overcome. He has found that when the exhaust port is opened on the expansion stroke the gases have a momentary impulse to bolt through the port in a body. This tendency lasts for a few thousandths of a second, and if advantage is taken of it more efficient charging and exhausting of the engine follows. No scavenging pumps, inlet pipes, or exhaust pipes are necessary to enable such an engine to run and deliver power.
The Kadenacy discovery shows that engineers have been too prone to conceive the motions of gases through engines as obeying the laws of continuously flowing fluids and that discontinuous, ballistic, or shooting motions are more important than they had imagined.
Text read from the printed page and cleaned; old type leaves the occasional error.