A NEW INTERPRETATION OF HORREBOW,CHRISTIAN SUNSPOT OBSERVATIONS FROM 1761 TO 1777

Christian Horrebow and his colleagues of Copenhagen, Denmark, actively observed sunspots from 1761 to 1777. These observations were examined by Thiele in 1859 and by d'Arrest in 1873 with markedly different con clusions. Thiele reported nearly twice as many sunspot groups as d'Arr est. To resolve this discrepancy, we have reexamined Horrebow's origin al notebooks. We find slightly more sunspot groups then did d'Arrest. Thiele apparently called individual sunspots sunspot groups, so he wou ld call a bipolar group two groups. d'Arrest seems to have missed coun ting some of the smaller sunspot groups. A correct interpretation of H orrebow's observations is required in efforts to reconstruct solar act ivity. Wolf gave a sunspot number for 1769 of 106.1. On the basis of o ur re-examination of Horrebow's drawings and other observers, we deduc e a sunspot number of about 80.5 for 1769.