274 



HISTORY OF SCIENCE. 



presents the appearance of a portion of the moon's crescent as seen 

 by a reflecting telescope, and exhibits clearly the crater-like depres- 

 sions. Maps of the moon were made by Hevelius, an astronomer of 

 Dantzig, and published in 1647. Cassini (J. D.) and T. Meyer pub- 

 lished charts in 1680 and 1749, and others have since appeared, of 

 which the most elaborate is Beer and Madler's, published in 1837. 



FIG. 128. 



A very slight attention bestowed on the appearance presented by 

 the moon, even to the naked eye, reveals the fact that the moon always 

 presents to us the same face. Of this face we see more or less as it is 

 illuminated by the sun, and with the telescope the same markings which 

 are distinctly seen on the full moon are visible in the part of the moon's 

 face illuminated only by the " earth-shine" when the moon presents 

 the appearance popularly known as "the old moon in the new moon's 

 arms." It must strike every person who considers this phenomenon as 

 a very remarkable circumstance, that the moon, in thus always pre- 

 senting the same side to the earth, should revolve about her own axis 

 in precisely the same time as she revolves about the earth. That the 

 moon does revolve about her axis is evident, if we reflect that to the 

 sun she presents, in succession, every part of her surface. It is neces- 

 sary to call attention to this, because some persons, considering only 



