The next steps would naturally have been to apply this technique to the detection and research of other particle types, including the Cosmic Rays newly discovered by Victor Hess in 1912. However, progress was halted by the onset of World War I in 1914. The outstanding issue of improving the particle detection performance of standard photographic emulsions, in order to detect other types of particle - protons, for example, produce about one quarter of the ionisation caused by an 𝛂-particle - was taken up again by various physical research laboratories in the 1920s.