Chap. IX.] SOLAR AND LUNAR GRAVITATION. 107 



solar tide and the solar counter- tide from the sun's 

 position (those tides corresponding with the meridian 

 of 6-i'' A.M. and 6 J'' p.m.), there will be a difference of 

 two hours in the relative distances of the lunar tides 

 from the moon's position. 



Therefore, though if the sun, moon and earth were 

 at rest, then the tides raised by the sun and moon 

 would be in conjunction at the same time as they ; 

 as the earth and moon are in motion, the tide 

 raised by the sun's gravitation as it revolves the earth 

 round the sun, and that raised by the moon's gravi- 

 tation as the earth revolves the moon round it, will 

 not be in conjunction when the sun and moon are in 

 conjunction, because the position of the solar tide 

 being 5^^ west of the sun's meridian, and that of the 

 lunar tide being 5^ east of the moon's meridian (for 

 the moon follows its tide), therefore the lunar tide 

 can only be in conjunction with^ the solar ti le when 

 the moon is 5^ west of the meridian of 6^^ a.m. — that 

 is, when the moon is on the meridian of 1^^ a.m. The 

 moon reaches this latter meridian in rather less 

 than two days after being in opposition to the sun. 

 Therefore, about two days after the sun and moon 

 being in opposition, the lunar and solar tides will be 

 in conjunction (as at CD in Fig. 2), their counter- 

 tides also being at the same time m conjunction on 

 the opposite side of the earth (as at r g). But also 

 when the moon is at the opposite point of its orbit 

 (as at n), two days after conjunction with the sun, 



