The sunspot.

Editor: J.S. Ricard.

Sunspot numbers, 1610-1985 : based on "The sunspot activity in the years 1610-1960" /

Mode of access: Internet.

Recherches astronomiques de l'Observatoire d'Utrecht.

Ceased with volume 18:2. Superseded by the Bullletin of the Astronomical Institutes of the Netherlands, Supplement series.