CONJUNCTION QUADRATURE, &c. 



of the snn, and E the earth ; when the moon is at N, between 

 the sun and the earth, its illuminated hemisphere being turned 

 toward the sun, its dark hemisphere will be presented toward the 

 earth ; it will therefore be invisible. In this position the moon is 

 said to be in coN-rracxiox. 



When it moves to the position c, the enlightened hemisphere 

 being still presented to the sun, a small portion of it only is 

 turned to the earth, and it appears as a thin crescent, as repre- 

 sented at c. 



7. When the moon takes the position of Q, at right angles to the 

 sun, it is said to be in QTTADRATITRE : one half of the enlightened 

 hemisphere only is then presented to the earth, and the moon 

 appears halved as represented at q. 



When it arrives at the position G, the greater part of the 

 enlightened portion is turned to the earth, and it is gibbous, 

 appearing as represented at g. 



8. When the moon comes in OPPOSITION to the sun, as een at 

 r, the enlightened hemisphere is turned full toward the earth, and 

 the moon will appear full as at f, unless it be obscured by the 

 earth's shadow, which rarely happens. In the same manner it is 

 shown that at G' it is again gibbous; at <j' it is halved, and at c 7 

 it is a crescent. 



If the moon or the planets be supposed to be viewed by an 

 observer placed on the one side or the other of the general plane 

 in which they move, they will appear to move either in the 

 direction of the hands of a clock, or in the contrary direction, 

 according to the side of the general plane from which they are 

 seen. If the observer be supposed to be on the north side of that 

 plane, their motion will be contrary to that of the hands of a 

 clock. If he is placed on the south side of that plane, their 

 motion will be in the direction of the hands of a clock. 



In the case represented in fig. 2, and also in the astronomical 

 diagrams in the first volume of the Museum, pp. 5, 11, &c., the 

 observer is supposed to be placed at the south side of the general 

 plane. 



9. In order to determine whether or not the globe of the moon 

 is surrounded with any gaseous envelope like the atmosphere of 

 the earth, it is necessary first to consider what appearances such 

 an appendage would present, seen at the moon's distance, and 

 whether any such appearances are discoverable. 



10. According to ordinary and popular notions, it is difficult to 

 separate the idea of an atmosphere from the existence of clouds ; 

 yet to produce clouds something more is necessary than air. The 

 presence of water is indispensable, and if it be assumed that no 

 water exist, then certainly the absence of clouds is no proof of the 



37 



