From the 1993 lecture programme:
Our ﬁve senses only reveal a small part of the large variety in the Universe. We cannot see molecules unaided (though our nose can smell particles much smaller than our eyes can see) and we only respond to the rainbow of colours — a mere octave in the infinite range of the electromagnetic spectrum. If we had a bee’s eyes we could see in the ultraviolet; we can feel infrared radiation as heat and occasionally one hears of people picking up radio signals in their dental ﬁllings. Our ancestors eyes developed to guard against attacks by dangerous animals; it was not important for them to see distant radio galaxies. Today, by means of infrared cameras, we watch for human prowlers in the dark and can look deep into the Universe, revealing much more than shows up in the tiny range of visible light.
An aim of the lectures is to open up a spectrum beyond the rainbow, towards smaller wavelengths which can see smaller things. Even with a powerful optical microscope we cannot resolve individual molecules. X-rays can resolve distances similar to the separation between molecules in a regular crystal, as in the discovery of the structure of DNA, but do not reveal the individual molecules.
Electrons, which are present in everything, provide access to distances smaller than X-rays can reveal. Electron microscopes in the laboratory can provide pictures of molecules, even of atoms. With a 2 mile long electron microscope we can even look deep inside an atomic nucleus.