(34 Eclipses of the Moon. 



consequence ; and we conceive that the explanation above sup- 

 plied is sufficient to account for all the phenomena of eclipses 

 which have been accurately observed. We have remarked that 

 the red colour appears much sooner when we remove from the 

 field of vision that portion of the moon''s disk which is already 

 bright. As by this step we only diminish the enfeebling opti- 

 cal effect of this portion on the other, without entirely destroy- 

 ing it, it is most probable that we should speedily remark the 

 red colour, could this optical influence be completely removed, 

 even should the vivacity of the colour be subsequently in- 

 creased. 



It is likewise to the influence of the terrestrial atmosphere 

 that Messrs B. and M. principally attribute the circumstance, 

 that, in eclipses of the moon, the pure shadow is somewhat more 

 extended than it should be, according to the dimensions of the 

 globe. Their observations of the entrance of many lunar spots 

 into the shadow during the eclipse of the year 1833, and of 

 their exit from the shadow, have yielded them, for the half of 

 the eclipse, a mean duration, greater than it should have been, 

 of from ninety-three to nine-five seconds of time, and a corre- 

 sponding augmentation of the semi-diameter of the shadow of 

 about a fiftieth part. In the partial eclipse of the 10th of June 

 1835, they found about a twenty-eighth part was the augmen- 

 tation of the semi-diameter of the shadow, resulting from the 

 comparison of their observations with the calculations. Lam- 

 bert estimated this increase at one-fortieth, and Meyer at one- 

 sixtieth. Messrs B. and M. also conceive, that this apparent 

 augmentation might partly be owing to the smallness of the 

 solar crescent which is seen upon the moon during eclipses, and 

 which, in certain cases, may cause the mixed, or imperfect 

 shadow, to be confounded with the pure one.* 



* Dr Miidler has published (in Astr. Nachr. No. 337) a memoir upon the 

 astronomical uses of a lunar chart, in which he supplies formulae for the cal- 

 culation beforehand, in lunar eclipses, of the moment of ingress of the princi- 

 pal spots into the shadow's cone, as well as that of their egress, and has ap- 

 plied them to the total eclipse of October 13. 1837. In this memoir he also 

 points out the spots which may be most advantageously examined in the de- 

 termination of the precise position of the rotatory axis of the moon, and for 

 ascertaining if this axis undergoes any real balancing as does that of the 



