by one, now by another assistant (though their names are not given), and a great deal of it was written by the above-mentioned Elias Olsen, whose writing appears in it for the last time in April 1589. Probably he left Tycho's service at that time, as he is mentioned in the diary as having arrived and departed several times after that date.[1]
In 1584 Elias Olsen was sent by Tycho on an astronomical expedition of some importance. At Hveen the inclination of the ecliptic had been found equal to 23° 31′.5, while Copernicus had found 23° 28′. Tycho correctly explained this by pointing out that Copernicus had measured the meridian altitudes of the sun at the summer and winter solstices without taking refraction into account, and for the latitude of Frauenburg in Prussia this would at the winter solstice cause an error of over 4′ in the altitude. Tycho, however, believed the solar refraction at the altitude of 12° to be equal to 9′; but, on the other hand, he assumed with Copernicus, that the solar parallax was 3′, so that one mistake is somewhat compensated by the other. He had also found that the solar theory of Copernicus often deviated considerably from the observed places of the sun, and he suspected that Copernicus had reduced his solar observations with an erroneous value of the latitude. He, therefore, gladly took an opportunity of verifying this latitude when, early in 1584, an embassy from George Frederic, Margrave of Ansbach,[2] headed by a nobleman of the name of Levin
- ↑ He was at Hveen June 9 to 11, and July 1 to 3, 1589, November 5 to March 11, 1590. Under the last date the printed edition has "Elias obiit H. 1112 noct.," but doubtless the original has abiit and not obiit, for the words "Elias Olai" occur again on the 8th May 1596, so he cannot have died in 1590. In 1589 he went with Vedel on a tour through Denmark to observe latitudes and azimuths for Vedel's topographic survey of the country. See E. O. Morsing og hans Observationer, af F. R. Friis, Copenhagen, 1889, 28 pp. 8vo.
- ↑ Regent of the Duchy of Prussia (for his cousin, Duke Albrecht Frederic, who was insane). The house of Hohenzollern is descended from him.
