360 



THE ILLUMINATION OF THE EOLTPRED MOON. 



knowledge goes, the clia-ractor of a lunar oclipse is per- 

 sistent throughout its duration. The light oclipsos are light 

 from first to last ; the dark eclipses are dark from first to 

 last. Unless, therefore, we suppose a number of remarkable 

 coincidences, we must believe that the particular condition 

 which determines the lightness or the darkness of an 

 eclipse is persistent through a length of time much ex- 

 ceeding the duration of the oclipse. If wo suppose this 

 condition to persist for twelve hours, and to bo seated in 

 the earth's atmosphere, it must be a condition involving 

 nearly the whole of the atmosphere. To suppose that the 

 atmosphere ovoi-, say, three-fourths of tlie gh)be can be 

 greatly more humid or greatly more cloudy at one time 

 than at another, would be manifestly unreasonable. 



It may possibly bo objected that the atmospheric ring 

 presented by the earth to the sun and moon in a lunar 

 eclipse may be very different in different eclipses as regards 

 the relative proportions of land and water underlying it, 

 and that its hygrometric condition, and therefore its trans- 

 parency, may vary considerably from that cause. 



I do not think this objection would weaken my argu- 

 ment materially, even were there no special reasons for 

 rejecting the explanation which it offers. But there are 

 two such reasons. 



In the first place, it rests on the assumption that the 

 lower strata of the atmosphere are those chiefly concerned 

 in transmitting the rays which illumine the eclipsed moon, 

 whereas I hope to show presently that that assumption very 

 imperfectly represents the real facts of the case. 



Secondly, the explanation will not bear the test of appli- 

 cation to the phenomena of actual eclipses. If we compare 

 the eclipses of March 19th, 184S, and October 4th, 1884, 

 with respect to the proportion of land and water underlying 



