A Foucault pendulum requires care to set up because imprecise construction can cause additional veering which masks the terrestrial effect. As observed by later Nobel laureate Heike Kamerlingh Onnes, who developed a fuller theory of Foucault pendulum for his doctoral thesis (1879), geometrical imperfection of the system or elasticity of the support wire may cause an interference between two horizontal modes of oscillation, which caused Onnes' pendulum to go over from linear to elliptic oscillation in an hour. The initial launch of the pendulum is also critical; the traditional way to do this is to use a flame to burn through a thread which temporarily holds the bob in its starting position, thus avoiding unwanted sideways motion (see a detail of the launch at the 50th anniversary in 1902).