The application of a strong magnetic field enables the measurement of the energy of the most penetrating particles to be carried out, and the method may be capable of still further extension and improvement.

Simultaneous recording with superimposed ionization chambers and Wilson chambers, ionization chambers and sets of counting tubes, has not yet been carried out.

The investigation into the possible effects of cosmic rays on living organisms will also offer great interest.

It may well be said that the answer to the question: Of what do the cosmic rays in fact consist before they produce their familiar secondary radiation phenomena in the earth's atmosphere? can only be obtained from numerous measurements in the stratosphere.

In order to make further progress, particularly in the field of cosmic rays, it will be necessary to apply all our resources and apparatus simultaneously and side-by-side an effort which has not yet been made, or at least, only to a limited extent.

From a consideration of the immense volume of newly discovered facts in the field of physics, especially atomic physics, in recent years it might well appear to the layman that the main problems were already solved and that only more detailed work was necessary.

On what can we now place our hopes of solving the many riddles which still exist as to the origin and composition of cosmic rays?