108 ECLIPSES. 



same meridian opposite the moon ; we are fifty minutes in 

 overtaking her, and the tides are retarded for the same rea- 

 son that the moon rises later on one day than on the pre^ 

 ceding. 



The tides, though constant, are not equal ; but are great- 

 est when the moon is in conjunction with the sun or in 

 opposition to it, or at the time of new and full moon ; and 

 least, when in quadrature to it. This increase and diminu- 

 tion constitute the sjjriiig and 7ieap tides. The attraction 

 of the sun does not raise tides ; its only effect is to increase 

 or diminish those of the moon. The tides are highest when 

 both the luminaries are in the equator, and the moon at the 

 least distance from the earth. This happens at the time of 

 the equinoxes. The tide is at the greatest height, not when 

 the moon is in the meridian, but some time afterwards, be- 

 cause the force by which the moon raises the tide continues 

 to act after it has passed the meridian. The regular tides 

 are greatly affected by strong winds. Continents also stop 

 them in their course from east to west, and in narrow rivers 

 they are frequently very high and sudden, from the resistance 

 of the banks. The advantages arising from tides are great. 

 By agitating the waters of the ocean they preserve them in 

 a state of purity. Aided by their means, ships of the largest 

 burden sail up rivers against their natural* course, and con- 

 vey into the interior of countries tliose productions which 

 stimulate the industry and promote the happiness of nations, 



Questions. — 1. What arc the tides? 2. How are they occasion- 

 ed .'' 3. How does it appear that the moon produces high water in two 

 places at the same time ? 4. How do you account for the tide being 

 fifty minutes later every day? 5. What are spring and neap tides? 

 6. What is the eifect of the sun's attraction ? 7. When are tides highest ? 

 8. What produces irregularity in tides ? 9. What advantages arise 

 from tides ? 10. Look at figures 42 and 43, and explain the tides. 



LESSON 49. 



Eclipses. 



An'nular, having the form of a ring, from annulus, a Latin "Word 

 for ring. 



The earth being an opaque body enlightened by the sun, 

 necessarily projects a shadow into the regions of space in a 



