28 Astronomy* [Lecture 24, 



must both be of the sun ; for in every year there 

 are at least two eclipses of the sun. 



There can never be more than three lunar 

 eclipses in a year ; and in some years there are 

 none at all. 



Though the number of solar eclipses is greater 

 than that of lunar, in the ratio of 3 to 2 ; yet 

 more lunar than solar eclipses are visible in any 

 particular place, because a lunar eclipse is visible 

 to an entire hemisphere, while a solar eclipse is 

 only visible to a part. 



Central eclipses are comparatively rare phae- 

 nomena; for though there are about 28 such 

 eclipses in every cycle of 18 years and 10 days ? 

 yet the terrestrial space over which every one of 

 them appears to be central, is a narrow belt, in 

 some cases a mere mathematical line traced across 

 the enlightened hemisphere of the earth. 



In all eclipses, whether of the sun or moon, 

 there are three points particularly to be observed, 

 the beginning, the middle, and the end; and 

 every precaution is taken to note the precise mo- 

 ment of each of these three phases. In total 

 eclipses there are two other circumstances to be 

 observed ; these are the total immersion and the 

 commencement of the emersion. In total eclipses, 

 then, there are five particulars to be observed, 

 the commencement of the immersion, which is 

 the commencement of the eclipse ; the total im- 

 mersion ; the middle of the eclipse ; the com- 



