Hendrik (Henk) Christoffel van de Hulst was always interested in almost everything. As a young boy he played chess and was very fond of all kinds of puzzles. When a jigsaw puzzle was too simple for him, he tried to complete it upside down. But very soon he also started to love literature and to enjoy the wonders of nature in a broad sense. It was not long before he discovered his mathematical skills and developed these to a high level, partly in school, partly all by himself.
Henk went to the University of Utrecht in the heart of the Netherlands in 1936 and started studying mathematics and physics. But very soon he was attracted more and more to astronomy by the clear and inspiring lectures of Marcel Minnaert, the well-known author of ''Light and Colour in the Open Air''. One of the other students in astronomy was Henk's future wife, Wil Mengerink. They first met on the roof of the observatory, where students had to conduct some observations as part of their practical exercises.
In 1941, Leiden University organized a prize competition for an essay. The question was to discuss critically the origin and growth of solid particles in the interstellar environment. Henk attacked the problem forcefully. He visited many libraries and read books as well as papers on physics, chemistry and meteorology; he took copious notes and finally submitted his essay in April 1942. The jury did not award the prize, but instead offered two honorable mentions, one for Henk, saying that his essay showed he had a ''mature scientific spirit''. Henk was only 23 years old at that time. One of the members of the jury was the famous Leiden astronomer Jan Oort, who was a master in getting talented people interested in astronomical problems. As a result, van de Hulst and Oort started collaborating on the problem of the growth of interstellar particles and that was the beginning of an association for life. But Henk also became very interested in the scattering of light by these interstellar particles and this was to become the subject of his thesis under the supervision of Minnaert. Oort suggested that he not just cite the results of Mie computations for light scattering by spherical particles, but to study Mie theory himself. Henk decided to do so and soon found himself writing chapter after chapter on Mie theory. Thus, this became the main topic of his Doctor's thesis which was entitled ''Optics of Spherical Particles'' and was finished in 1946. It was a brilliant piece of work and the degree of Doctor was awarded with the highest honours. The thesis material formed the basis for van de Hulst's book on ''Light Scattering by Small Particles'', which was first published in 1957 and republished in 1981 as a Dover book. This book became extremely popular among scientists in a variety of disciplines. It was not only a comprehensive, unifying treatment of the subject, but also contained important new results in areas where little or nothing had been done before. The lucid style of the book is remarkable and inspiring. Arguments based on physical intuition are given wherever they illuminate the subject more clearly than a mathematical derivation.
During the Second World War Holland was occupied by Germany and life was difficult for most people. Almost no scientific news from abroad reached Holland and communications gradually dwindled to almost nothing. But Oort knew that cosmic radio emission had been discovered in the USA and he said: ''If there were a spectral line which we could measure, then the Doppler shift could be used to map the motions in the Galaxy''. Oort asked Henk in 1944 to investigate this and after spending several months on a theoretical study