NO. 9 BRIGHTNESS OF LUNAR ECLIPSES FISHER 4I 



curve is drawn amid a cloud of observation points, and its form 

 is unavoidably somewhat arbitrary. As the depressions count in 

 forming the denominators, the curve rises often above lOO per cent. 

 Beside minor variations, there are three very deep depressions, which 

 follow certain volcanic catastrophes, and are named from them : 



Krakatoa depression, 1883 VIII to 1886 XII. 



Pelee depression, 1902 VII to 1904 X. 



Katmai depression, 1912 III to 1924 VI. 



On account of the peculiarities of the method, the dates of begin- 

 ning and ending of these depressions can be only roughly stated ; e. g., 

 the Krakatoa depression seems to have been well started by the end 

 of 1882, though Kimball begins it with the month of the eruption. 



This curve is copied in figure i of this paper. 



During these volcanic depressions there were lunar eclipses as 

 shown in table 6. 



Table 6. — Relation of Volcanic Haze and Brightness of 10 Lunar Eclipses 



Depression Date Path Magn. Grade 



Krakatoa 1884 IV 9 C 1.44 0? 



1884 X 4 C I.S3 I 



188s III 30 N 0.89 1 



Pelee 1902 X 16 C 1.46 i 



1903 IV II N 0.97 



1903 X 6 S 0.87 2 



Katmai 1912 IV i N 0.19 i 



1913 III 21 C 1.58 



1913 IX 14 C 1.44 



1914 III II S 0.92 2 



Summaries; Eclipses 1880-1922 



Nvimber 



Sum of Mean 



grades grade 



I. All included : 



In depressions 10 8 0.80 



Not in depressions 42 57 1.36 



II. Southern excluded : 



In depressions 8 4 0.50 



Not in depressions 28 23 i-i8 



III. Southern only : 



In depressions 2 4 2.00 



Not in depressions 14 24 1.73 



Taking all the 10 eclipses occurring during depressions, mean 

 grade 0.80, and comparing with the 42 eclipses, mean grade 1.36, 

 not in depressions but in the period 1880- 1922 which surrounds the 

 depressions, the eclipses in the depressions average much dimmer 

 than those without. But 2 of those within are southern eclipses, 



