The difficulty of finding a mechanism by which sunspots could produce such strong magnetic fields as are always associated with them has led to a new theory of sunspots, according to which the magnetic field of the spot is the primary phenomenon. The other properties of a spot ( e.g. the low temperature) are found to be due to the effect of the magnetic field on the solar atmosphere. As a spot magnetic field cannot be produced near the solar surface, it is supposed to originate near the Sun's centre and to be transmitted outwards along the magnetic lines of force of the Sun's general magnetic field in the form of a new type of wave, called the magneto-hydrodynamic wave. A brief survey of this theory is given in sections 1 and 2. According to the theory the wave from a disturbance near the solar centre first reaches the solar surface at high latitudes and later proceeds towards the equator. As this explains the progression of the sunspot zone, it is of interest to compare the theory and observations in detail. Sunspot observations are therefore treated in order to derive a certain curve, the “sunspot zone progression curve”, which shows the regular displacement of the spot zones (sections 3 and 4). Comparison of this curve with the theory permits some conclusions regarding the Sun's general magnetic field (sections 5–8).