The Behaviour of Solar Activity as Inferred from Sunspot Observations 165 BC to 1986

Wittmann, A. D., & Xu, Z. T. (1988). The Behaviour of Solar Activity as Inferred from Sunspot Observations 165 BC to 1986. In Secular Solar and Geomagnetic Variations in the Last 10,000 Years (pp. 131–139). Springer Netherlands. https://doi.org/10.1007/978-94-009-3011-7_8