Astronomy. [Lecture 20. 



so much, even in her quickest descending lati- 

 tude, as not to allow us still the benefit of her 

 rising nearer the time of sunset for a few days 

 together about the full in harvest, than at any 

 other time of the year. 



The moon, when viewed through a telescope, 

 presents a vast irregularity of surface. These 

 inequalities are most apparent at the edge of her 

 enlightened part, when she is not at or near the 

 full ; for the sun's rays are intercepted by the 

 hills or prominences, so as to give that part of 

 her surface a jagged appearance : and sometimes, 

 to show the luminous tops of mountains, at a 

 considerable distance from the illuminated disc. 

 Upon mathematical principles, some of these 

 prominences have been measured, and one of 

 them is computed to be at least three miles in 

 height. 



.Maps of the moon, have been published, and 

 her surface fancifully divided into lands and 

 seas, and names were even assigned to both. 

 The more correct discoveries, however, made 

 with the powerful glasses of Dr. Herschell, have 

 dissipated these pleasing illusions. Those parts 

 which were formerly supposed to be seas are now 

 found to be only cavities or valleys, which re^ 

 fleet the light less strongly than the more ele- 

 vated parts. Through these instruments, in 

 fact, the moon appears a mere volcanic mass, 

 without water or atmosphere. That the moon 

 has no atmosphere has by many been thought 



