 François and Pieter developed their ability to build and tune carillons in close cooperation with Jacob van Eyck (±1590-1657), a musician and composer who developed a method of precisely identifying the overtones of bells.Van Eyck, appointed city carillonneur of Utrecht in 1642, had drawn the attention of leading scientists of his day, such as Christiaan Huygens (his relative) and René Descartes, with his ability to isolate five partials of a bell by whistling to create sympathetic resonance.When struck, a bell produces a number of partials which, if imprecisely tuned, can create an unpleasant sound and which prevents it from harmonizing in accordance with other bells.