go THE HAMILTON ASSOCIATION. 
In going through these phases the moon more than completes 
the circuit of her orbit around the earth, for the earth during a luna- 
tion is carried forward in its movement around the sun about 30 
degrees, and the moon must pass over that distance before sun, 
moon and earth take the relative positions requisite to make new moon. 
Such a lunation, or course of the moon once round the earth, and 
far enough on a second course to come again in conjunction with the 
sun, 1s called the moon’s synodical revolution. ‘The mean time for 
making it is 29 days, 12 hours, 44 minutes and 3 seconds. The 
mean time it takes for the circuit of her own orbit only is but 27 days, 
7 hours, 43 minutes and 11 seconds. ‘Thus in each lunation the 
moon, from the earth’s motion of translation round the sun, proceeds 
2 days, 5 hours and 52 seconds on a second course before coming 
into the necessary alignment with sun and earth essential to present 
the phenomenon of new moon. These figures furnish the mean 
time in which the moon is carried through her orbit, but disturbing 
forces so considerably affect her velocity and direction, that astrono- 
mers, only by long profound research, have succeeded in foretelling 
what will be the moon’s place in the heavens at any given future time. 
Astronomical science regards the heavenly bodies in two aspects : 
in their relations to time and space, and as masses of matter moving 
in obedience to cosmical forces. Ages of observation prepared the 
way for the latter conception, and ancient astronomy chiefly kept 
watch over the times and seasons. Still, in the early stages of astro- 
nomical research, the moon was accorded attention, as many ancient 
nations used the moon’s phases as a measure of time. The word 
moon, it is thought by some philologists, can be traced to the root 
ma, Meaning to measure. 
Although a lunation is, in many respects, a desirable standard 
for measuring time, it has been found extremely difficult to make it 
a sub-division of the tropical year, or the time taken by the earth to 
complete her course from, and return to, the vernal equinox. Where- 
ever the lunisolar year has been adopted intercalations have been 
necessary to bring the lunar months and solar years out even. The 
Greeks used simultaneously the two standards, and had no end of 
difficulty to keep them from overlapping. Their Olympiads supply 
a record for a thousand years, and are perhaps the best scale of past 
events on record. They originated from holding, every four years, 
