From the 1993 lecture programme:
We are being invaded by extraterrestrials. The nuclei of atoms produced in deep space are whirled by electric and magnetic forces in the galaxy until, trapped by the Earth’s magnetic arms, they smash into the upper atmosphere far above our heads. Fragments rain down: millions of cosmic particles pass through our bodies all the time and, by means of spark chambers, we can expose them to view. The sparks show where particles smaller than atoms — such as electrons, protons, atomic nuclei — have passed by.
Occasionally, if you are lucky, you may see these particles produce matter from energy — E = mc2 at work. Cosmic rays show that there are things in the Universe that we didn’t know existed. To understand these essential pieces in Nature’s jigsaw we need to produce intense versions of the cosmic rays here on Earth and photograph efficiently what happens. This brings us to the era of the high energy particle accelerator and to the beautiful images of the bubble chamber. The abstract art trails in bubble chamber photographs are like hieroglyphics that reveal the secrets of the Universe. They lead us to discover that deep inside all matter are bizarre particles called “quarks”. And with the aid of a huge electron microscope we can even capture direct evidence of these ultimate particles, among the first inhabitants of the Universe.