NO. 9 BRIGHTNESS OF LUNAR ECLIPSES — FISHER 35 



c=:i.4 6y2 inch reflector; during mid-eclipse all maria were conspicuous 

 both in telescope and to n. e. Most of the brightest craters, including 

 Tycho and his ray system, Copernicus and the Alps, were easily seen 

 with the telescope. 

 Heath, Kingsbridge, Engl., (319) ; at first, haze and corona; later clear. 



c = 1.4 zYs inch ; all the lunar maria prominently visible in the eclipsed portion. 



Tycho neither it, nor most of its bright streaks, became 



invisible at any time. 



Meyermann, Gottingen, Ger., (322) ; good air conditions. 



c ^ 1.4 13.8 cm. ; even during the maximum phase of the eclipse all seas 

 were clearly recognizable, particularly notable Mare Humorum and 

 Mare Tranquilitatis. Grimaldi was a very noticeable dark spot. Cen- 

 sorinus, Menelaus, Manilius, Aristarchus, Tycho, of which two rays 

 were especially bright, were easy to make out ; Copernicus and Kepler, 

 difficult. 



Since Kepler, the visibility of the totally eclipsed moon has been 

 laid to refraction of light by the earth's atmosphere into the geometri- 

 cal umbra; of late years, since the researches of Tyndall, Raleigh I 

 and others on the blue of the sky, scattering of light into the umbra 

 by dust and air molecules has been added. At the time of the Krakatoa 

 sunsets the attention of all was directed to the results of dust in the 

 air; the dim eclipse of 1884 X 4 caused the suggestion to be made by 

 several^ that the classical explanation of dark eclipses — cloudiness 

 along the terrestrial terminator — should be at least supplemented by 

 opacity due to the same causes which produced the strange twilight 

 glows. Duf our and Johnson ^ called attention to the coincidence of 

 dark eclipses with volcanic dust haze, as in 181 6, after Temboro, 181 5. 

 The dark eclipse of 1903 IV 11, after the West Indian and Guatemalan 

 eruptions of 1902, brought this explanation to the fore. But other 

 suggestions for the varying brightness of the eclipsed moon have 

 been made ; the moon's varying distance, from perigee to apogee ; 

 the moon's longitude, whereby, she being near an equinoctial point, 

 vernal or autumnal, the refracted light comes largely from the Arctic 

 and Antarctic polar regions, supposed to have purer and more refrac- 

 tive air, while, near a solstitial point, the terrestrial terminator passes 

 close to the Arctic and Antarctic circles of latitude, and the light 

 comes through more cloudy regions of the atmosphere. This sugges- 



^ I do not know to whom priority should be assigned ; S. J. Johnson, Mon. 

 Not. Roy. Astr. Soc, 45, pp. 43-44, 1884-5, and G. F. Burder, Nature, 30, pp. 

 590-591, 1884, were among the first. 



* Ch. Dufour, Bull. Soc. Astr. Fr., i, pp. 58-60, 1887, L'Astronomie, 7, pp. 

 28-30, 1888. 



S. J. Johnson, Mon. Not. Roy. Astr. Soc, 63, pp. 400-402, 1903. 



