SECTION J       GENERAL PHYSICS

Steinheil Sohne (Munich)
They were producing large rock-salt crystals for infra-red lenses, by allowing small crystals to grow inside a low temperature spiral. About 10 hours was required to grow a crystal sufficiently large for a 14 cm. diameter lens. Annealing took a similar time. The lens was polished with chrome oxide. The firm had also experimented with lithium fluoride, thallium bromide, barium and strontium chlorides. The latter chlorides were thought to be best for infra-red work.

The above firm were also experimenting with a new type of electrical amplifying device, which consisted simply of a layer of a semi-conductor on glass. The grid to which the modulating potential was applied was a plate which was very close to the semi-conducting layer to give a high potential gradient. The current passing through the semi-conductor varied with the potential on the grid i.e. on the concentration of free electrons at the surface of the film.

Steinheil Sohne were also producing semi-reflecting films with extremely low absorption. Titanium oxide was found to be the best substance, deposited on glass by evaporation. Extremely low absorption was obtained with films giving equal transmissions and reflections. A sample was obtained.

Askania. Constance The firm were developing a course steering device for aircraft. A magnetic compass, suspended in air, provided a line fixed in the earth's magnetic field. An arrangement of air jets round the compass could be set for the desired course. If the course changed, the pressure from the air jets became unbalanced, thus precessing a gyroscope which operated a servo-motor acting on the rudder.

Dr. Strughold. Gottingen The use of light as a weapon was being seriously considered by the Germans. It had been shown that occulting a light at a frequency of approximately 4 c./sec. caused a considerable deterioration of vision. It was intended to use this fact in defensive A.A. measures.