IS THE MOON A DEAD PLANET?, 571 



the crater named Messier by Beer and Madler. In its equatorial re- 

 gion, on the westernmost of the great lunar plains, close to one an- 

 other, are two small crater-plains about nine miles in diameter, sur- 

 rounded by very low ridges and mounds and crater-like depressions. 

 These two formations, named Messier and Messier A, were discovered 

 and described by Schroter, who regarded Messier as slightly the larger. 

 Beer and Madler examined these formations most carefully on more 

 than three hundred distinct occasions between 1829 and 1837. They 

 declared that the two crater-plains were exactly alike in every par- 

 ticular. Both were circular and of the same size, with bright, grayish- 

 white walls and a yellowish-gray interior. The walls were of the 

 same height, with wall-peaks situated in the same relative position. 

 In diameter, form, height of walls above the surrounding surface, and 

 depth and color of the interior of the walls, Beer and Madler declared 

 that they were completely alike. Some years after this, a slight dis- 

 similarity between the forms of the two craters was noticed, and in 

 November, 1855, the Rev. T. W. Webb, one of the best living lunar 

 observers, discovered that the eastern crater-plain, Messier A, ap- 

 peared the larger of the two. 



In March of the following year he observed that not only was 

 Messier the smaller, but that it was elliptical. He confirmed these 

 observations on repeated occasions, and in 1857 made drawings show- 

 ing Messier A unchanged, while Messier had an elliptical form, with a 

 long diameter of about 10 or 11 miles and a short diameter of about 

 7| to 8 miles. The matter attracted little further attention until 1870 

 to 1875. During these vears Messier and Messier A were studied with 

 the aid of powerful telescopes, and during the past year the long 

 diameter of Messier appears to be 12.2 miles and the short diameter 

 6.9. The difference between the form and dimensions of these two 

 formations is now obvious in the smallest astronomical telescope. It 

 is inconceivable that Beer and Madler could have failed to recognize 

 these differences with their fine Frauuhofer equatorial, with which, on 

 hundreds of different occasions, they carefully scrutinized them in 

 search of differences. 



This slow squeezing out of shape of an immense crater-plain is a 

 change that seems to defy explanation. Nothing analogous now 

 exists on the surface of the earth, and it is not surprising that there 

 should be a strong reluctance to admit that such a change has oc- 

 curred. A careful examination of Messier and its neighborhood, how- 

 ever, suggests that, instead of a bodily compression of the entire 

 crater, 'Miere has been a gradual sliding of the north and south walls 

 into the interior, and a pushing of the entire western wall outward 

 and westward down an incline existing there. Stenographers could 

 point to a hundred cases where a like circumstance has occurred. As 

 far as is at present known, this explanation accords with the condi- 

 tion of the formations around Messier, but further observations with 



