Eclipses of the Moon. 6S 



was wholly invisible during the great erpart of the total eclipse, 

 although it did not pass towards the centre of the shadow. 



It would appear that these striking differences are not owing 

 to the greater or less dimensions of the section of the cone'*s 

 shadow which traverses the moon, nor to its distance from the 

 centre of this section. According to Messrs B. and M., they 

 depend, to a great extent at least, on the state of the terrestrial 

 atmosphere in the regions where the sun rises and sets at the 

 time of the eclipse, the sun*s rays being refracted by the hori- 

 zon of these regions, so as to be propagated even to the moon, 

 with the various shades of colour belonging to our twilight. 

 As it is easy to calculate in each case what is the terrestrial 

 zone to which the sun''s rays are tangents, and in what part 

 of this zone the inflection of these rays will direct them to- 

 wards the moon, we may determine before hand, in certain 

 cases, and to a certain extent, the general circumstances of an 

 eclipse in these matters; and still more may ascertain afterwards, 

 if there has been an accordance between the circumstances of 

 the terrestrial atmosphere and the appearances which the eclipse 

 presented. It was thus, that, during the eclipse of June 10. 

 1816, the refracted solar rays which could reach the moon must 

 have traversed the southern portion of the zone of contact {tan- 

 gence), w^hich was then in its winter, and almost entirely ocea- 

 nic, so that the invisibility of the moon might easily be explained 

 by the probable haziness of this part of the earth''s atmosphere. 



The feeble visibility, and the subsequent disappearance of a 

 particular region of the moon, observed by Eule in Dresden, 

 during a total eclipse in tli^e year 1818, may be explained by the 

 momentary brightening of some parts of the zone of contact. 



In conclusion, Messrs B. and M. remark, " we will not 

 venture to determine, as some individuals have done, whether, 

 at these periods, the moon exhibits a light which belongs to 

 itself, and which endows it in all cases, at the end of a certain 

 time, with a red tint. Hahn admits, that in any lunar region 

 there is always, when it is illuminated with sufficient directness, a 

 kind of phosphorescence which we cannot perceive except during 

 eclipses ; and he moreover Mieves that the surface of the moon 

 receives from the sun a greater quantity of light, and a less 

 quantity of heat than the earth. The latter of these statements 

 is probably true, while the former is by no means a necessary 



