330 FERGUSON'S LECTURES. 



LECT. sign. Therefore, 4. The moon can be but once a year 

 ^^^ opposite to the sun, in any particular part of the 

 ecliptic. 5. That the moon is never full but when she is 

 opposite to the sun, because at no other time can we see 

 all that half of her, which the sun enlightens. 6. That 

 when any point of the ecliptic rises, the opposite point 

 sets. Therefore, when the moon is opposite to the sun, 

 sh must rise at sun-set. 101 7. That the different 

 signs of the ecliptic rise at very different angles or de- 

 grees of obliquity with the horizon, especially in con- 

 siderable latitudes ; and that the smaller this angle is^ 

 the greater is the portion of the ecliptic that rises in 

 any small small part of time; and vice versa. 8. That, 

 in northern latitudes, no part of the ecliptic rises at so 

 small ac angle with the horizon, as Pisces and Aries do ; 

 therefore, a greater portion of the ecliptic rises in one 

 hour, about these signs, than about any of the rest. 

 &. That the moon can never be full in Pisces and Aries 

 but in our autumnal months, for at no other time of the 

 year is the sun in the opposite signs Virgo and Libra. 



These things premised, take 13J degrees of the 

 ecliptic in your compasses, and beginning at Pisces, 

 carry that extent all round the ecliptic, marking the 

 places with a chalk, where the points of the compasses 

 successively fall. So you will have the moon's daily 

 motion marked out for one complete revolution in the 

 ecliptic (according to 2 of the last paragraph.) 



Rectify the globe for any considerable northern lati- 

 tude, (as suppose that of London) and then, turning 

 the globe round its axis, observe how much of the hour- 

 circle the index has gone over, at the rising of each par- 

 ticular mark on the ecliptic ; and you will find that seven 

 of the marks (which take in as much of the ecliptic as 



Note 101. This is not always true, because the moon does not keep 

 in the ecliptic, but crosses it twice every month. However, the difference 

 need not be regarded ia a general explanation. Nota by tJie Author. 



