CHRONOLOGY, 
lunar and solar years, which have been 
mostly in use, and an acquaintance with 
which is of most consequence in chrono- 
logy, it will be proper just to notice some 
combinations of years which are mentioned 
in ancient history, and therefore proper to 
be known. 
Lustra. The Romans sometimes reckon- 
ed by lustra, a period of five years, which 
derived its name from a census instituted 
by Servius Tullius, which was to be paid 
by the Roman people every fifth year. 
The Olympiads were, however, the most 
remarkable of these combinations. They 
consisted of four Grecian years, and de- 
rived their names from the public games 
celebrated every fourth year at Olympia, 
in Peloponnesus. These games were insti- 
tuted in honour of Jupiter, but at what 
time, or by whom, is not known. After 
they had been neglected and discontinued 
for some time, they were restored by Iphi- 
tus, King of Elis, in the year B. C. 776; 
and it is from this date that the olympiads 
are reckoned in chronology. 
Cycles are fixed intervals of time compos- 
ed of the successive revolutions of a certain 
number of years. The lustra and the olym- 
piads may perhaps be included under this 
name, but the term is more commonly ap- 
propriated to larger intervals, connected 
with the periodical return of certain cir- 
cumstances and appearances. The great 
use made of cycles in chronology requires 
that they be particularly noticed. 
From the defective nature of the Greek 
calendar, the Olympic year, as it has been 
called, was subject to considerable varia- 
tion; and, from the retrocession of the 
months, which it occasioned, producing a 
gradual change of the seasons when the 
games were to be celebrated, led to much 
inconvenience. Cleostrates, a mathemati- 
cian of Tenedos, endeavoured to give it a 
more perfect form by inventing a cycle of 
eight years : this, Iiowever, being com- 
puted by lunar years, still left the calendar 
subject to great inaccuracies. To rectify 
these, Meton, a mathematician of great 
celebrity invented — 
The Lunar Cycle, a period of nineteen 
solar years, at the end of which interval tlie 
sun and moon return to very nearly the 
same part of the heavens. This improve- 
ment was at the time received with univer- 
sal approbation; but not being perfectly 
accurate, was afterwards corrected by 
Eudoxus, and s\ibsequently by Calippus, 
whose iinprovements modem astronomers 
have adopted. 
The use of this cycle was discontinued 
when the games, for the regulation of wliich 
it was composed, ceased to be celebrated. 
Tiie Council of Nice, however, wishing to 
establish some method for adjusting the 
new and full moons to the course of the 
sun, with the view of determining the time 
of Easter, adopted it as tlie best adapted 
to answer the purpose : and from its great 
utility, they caused the numbers of it to 
be written on the calendar in golden let- 
ters, which has obtained for it the name 
of the golden number. The golden num- 
ber for any year is found as follows : — The 
first year of the Christian aera corresponds 
to the second of this cycle ; if then to a 
given year of this aera one be added, and 
the sum be divided by 19, the quotient will 
denote the number of cycles which have 
revolved since the commencement of tlie 
Christian aera, and the remainder will be 
the golden number for the given year. e. g. 
If the golden number of the present year 
(1808) be required, one being added, the 
sum will be 1809 ; this being divided by 19, 
will give 9.5 for the quotient and 4 for the 
remainder, or golden number sought. 
The Solar Cycle is another of these pe- 
riods, the inventor of which is at present, 
however, unknown. It consits of 28 years, 
at the expiration of which, tlie son returns 
to the sign and degree of the ecliptic which 
he had occupied at the conclusion of the 
preceding period, and the days of the 
week correspond to the same days of the 
month as at that time. It is used to deter- 
mine the Sunday, or dominical, letter, which 
we shall briefly explain. 
In our present calendars the days of the 
week are distinguished by the firs,t seven 
letters of the alphabet ; A, B, C, D, E, F, 
G; and the rule for applying these letters, 
is invariably to put A for the first day of 
the year whatever it be, B for the second, 
and so in succession to the seventli. Should 
the first of January be Sunday, the domi- 
nical, or Sunday letter for that year will be 
A, the Monday letter B, &c. and as the 
number of the letters is the same as that of 
the days of the week, A will fall on every 
Sunday, B on every Monday, &c. throughout 
the year. Had the yeau' consisted of 364 
days, making an exact number of weeks, 
it is obvious that A would always have 
stood for the dominical letter : the year 
containing, however, one day more, it fol- 
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