Ihe Tides. 229 



fleeting the earth's force, and in the endeavor to overcome the 

 superior force of gravity the waters are thereby depressed shortly 

 before being presented ta the point of activity and hence are pre- 

 pared to leap forward to meet the moon at its transit as the tides 

 are known to do. 



The centrifugal force is greatest in the plane of the moon's or- 

 bit and diminishes towards the poles of rotation in proportion to 

 the cosine of the angular distance so that at the distance of 60 

 degrees it is reduced to one half. The centrifugal force of a 

 rotating sphere is everywhere parallel to the plane of the equator; 

 the components of this force at any point are: a force acting in 

 opposition to gravity and a force at right angles to the same, hav- 

 ing a tendency to move matter towards the equator. This is the 

 case with the tides, for no sooner have they formed, in fact during 

 their formation, they depart toward the equator. 



To follow the recurring impulse upon the tides as they depart 

 from their origin on their respective journeys must here be 

 omitted for want of time, by comparing the cotidal lines on the 

 chart with the moon's hour at the top and bottom of the chart, 

 the effect can ea-ily be traced. 



In order to connect several other features of the tide with this 

 tide-producing force, it will be necessary to define more closely 

 the moon's position and the variable orbit which she pur.-ues. 



The moon's orbit is inclined to the plane of the ecliptic about 

 5j degrees so that her latitude cannot exceed this quantity, but 

 the earth's equator is inclined 2S° 26' to the ecliptic, thence the 

 moon's declinUions will vary from to 23° 40' north and south 

 of the equator. The maximum declinations also vary by twice 

 the latitude by reason that the nodes of the orbit are not constant 

 but have a retrogade motion so that the moon may occupy every 

 possible position in a zone of 10° 40'. The declinations will be 

 greatest when the line of nodes coincides with the equinoctial 

 line, for here the earth's declination plus the moon's latitude will 

 be the moon's declination. These maximum declinations coincide 

 with the moon's quadratures at the equinoxes and with the 

 syzygies at the solstices, and vary between these points in the 

 interval. 



