The central fumre represents the Mtrons phases. around the Earth 

 \placcd in the centre the elliptical line AAAA. indicates thepcithi 

 of the Moon revolving from west to east, at eight points in 

 her orbit. The Moon is shown of her exact relative size to the, 

 Earth , her distance is however about ten times areater in pro 

 portion: within the lunar orbit the Moons phases tire repre, 

 cntcd on an enlarged disk . in order to show the principal spots 

 The Moon is the "sateltite of the Earth, that is .whilst the 

 Earth performs its annual revolution round the Sun . the 

 Moon accompanies ihe Earth, revolving also around it. The 

 Moon's orbit is an ellipse me Earth ol'cupving one of the 

 foci -its excentricitv is about 47 3O leagues "the mam dis- 

 tance Icing aboid 86000 leagues. From the figure of her 

 orbit the "Moon is sometimes nearer than at others:the 

 point at which she is nearest is ?/// -Perig-ee ifig-.l.P. 

 that at which she is farthest -Ayagee fig.l.A.'Thefcri 

 -ace and Apogee advance e\-er\' v ecu- about 4O?41'.46': 

 from west to east. TJie plane" of me lunar orbit makes 

 an angle of 5? 8'. 49" with the ecliptic, fig A. 'The planes 

 of the two orbits are ait bv a line passing through the 

 centre of the Earth, the two points where tAis line meets 

 the Moons orbit arc me ^soAesrone.thf ascending node, 

 when the Moon rises above the ccaptic towards me north 

 the other, the descending node, when she sinks below it to- 

 wards the south.' see fig-. 5 .The nodes advance every year 

 about 19? 20'. 29'.' in an opposite direction to her orbicular 

 \ motion. Let tfic Jfoon.'L.ng.&be atapoint of her orbit 

 L.n. below the ediptic. advancing towards her ascendino 

 node, the Suns attraction will be in tfie directwni.S. tKe 

 intensity of this force being represented bv the line L.&.it 

 ,may be decomposed into two forces- one. L.T. towards the 

 centre of the Earth, the other. L.m.. towards the plane of the 

 ecliptic , the action of these two forces would give the Moon 

 an intermediate^ direction. L.K.o,and cause her to cross soon- 

 -er the plane of the ediptic . The arc described above the ho 



T. fig. 2. sees the Sim at S. on the tropic of Capricorn & the Moon 

 ] at L.on the tropic of Cancer, the line of our horizon JLtLfkows 

 that the arc described above it bv the Sun is ven' small, whilst 

 that described by the Moon is very extended. One complete re\-ol\ 

 ution of the Moon round the Earth . that is. from one point of her 

 orbit to the sonic point aqain.is called a Periodical revolution and 

 is performed in 27 days. 7^hours. 43 minutes. 4% seconds. -Now suppos- , 

 ino, the Moon L.fig 1 .!^ at the bec/innina of her revolution.to be in con- , 

 -junction i.e. between me Sun\md theEartli.& that these three bodies 

 and a star E. arc on the same line R.E.- at the end of her revolution 

 the Eartli havino, advanced in its orbit, she will be at n in the plane x.z\ 

 parallel to R.E. to be again in conjunction she must therefore describe ^ 

 on the arc n. L.a nianbcr of degrees equal to the arc T. \..or R.M.des- 

 \-cribed bv the Earth . The Svnodical revolution or Lunar month is the m- 

 -terval "from one 'conjunction to another, a. period of 29 days.T2 hourt 

 44 minutes. 3 seconds. 



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