224 Obscurations of the Sun. 



April, 1547. According to a tradition reproduced by Kepler 

 from a passage of the Cosmo- Gritico of Cornelius Gemma, the sun 

 was so enfeebled for three days, that the stars appeared. In 

 a note on this subject (Gomptes Rendu s, t. lx., p. 653), M. Faye 

 has shown the unlikelihood of such a phenomena. Neverthe- 

 less, the recital of Kepler rests on something real, and by 

 research amongst contemporary witnesses, the explanation is 

 discovered. There was certainly, about the 24th April, 1547, 

 the day of the battle of Muhlberg, an obscuration — that is to 

 say, a mist of fog obscuring the sun and the moon, according 

 to Gemma Frisius.* As for the appearance of stars, Cor- 

 nelius Gemma does not say that he or his father saw them, 

 which would have given his assertion great value. He appears 

 to have borrowed the statement from Be Meteoris, of Frytsch, 

 of Lanbach, who first mentioned it. 



" According to Frytsch, it was on the 12th April that the 

 stars were seen, and it was exactly on this day that the planet 

 Venus was at her maximum of illumination, and up to the end 

 of the month she remained under conditions favourable to her 

 being seen in full day. The unusual appearance of Venus, 

 close to the time of the obscuration which occurred a few days 

 later, seems to have been the veritable foundation of the story, 

 which Kepler accepted the more readily, as it tended to con- 

 firm his theories. 



" I have studied various phenomena of obscuration, and a 

 comparative view of them leads us to refer them to a particular 

 state of the atmosphere, known as a dry fog. The origin of 

 these fogs is quite uncertain. They are commonly ascribed to 

 volcanic exhalations, and they may likewise be due to meteoric 

 dust suspended in the air, and diminishing its transparency. 

 But, whatever may be their cause, the connection between 

 them and the obscurations is not doubtful ; and to explain the 

 latter we need not have recourse to gratuitous hypotheses, such 

 as perturbations in the photosphere, occultations of the sun by 

 a cosmical mass, or by a cloud of asteroids." 



* Eeinier Gemma, the father of Cornelius, so called from his birth-place, 

 Friesland. 



