Royal Society. 273 
where a rubrick to direct how to find this reputed full moon, 
and what is the ufe of the golden number. The difference of 
the ecclefiaftical account in the Paichal tables, from that of the 
heavens, both as to the Eqninon: and full moons arifes hence. 
I. The common Julian year, by which we reckon, of 5^5 days 
and 6 hours, is lomewhat too long 5 being about 11 minutes of 
an hour longer than the true folar year j by reafon whereof, the 
Eqimwx; and other annual feafons, go forwards about 11 mi- 
nutes every year 5 which from the time of the Ato;/^ council 
till now, amounts to about 11 days 5 fo that the Equinox^ 
which then happened March 11^^ is now come back to our 
3{arcb loth ^ which upon Pope Gregory's reforming the Roman 
calendar, above 100 years fince, caules the difference of 10 
days between what we call the new ftyle and the old. 2. It 
was then fuppofed, that in 19 years, which is the compafs of 
the golden number, the lunations of new -moon and full-moon 
did return to the fame day and hour, as they were 19 years 
before 5 but tho' this be pretty near the truth, yet it comes 
fliort by about an hour and a half, which hour and a half m 
every 19 years, doth, fince that time, amount to four or five 
days 5 whence it happens, that the reputed full moon is later 
by four or five days, than that of th? heavens 5 but our Eafter 
is reckoned according to the reputed full -moons, derived from 
the golden number, and not according to thofe of the heavens. 
jin extraordinary Rainbow at Chefler 5 by Mr, Edm. Halley 
Phil. Tranf. N° 240. p. 193. 
AUGU ST 6^^ 1(^98, between 6 and 7 o'clock in the even- 
•" ing, Mr. Ralky obferved an /m, exceedingly vivid as to 
its colours, atfirft on the fouth fide only, but in a little time 
with one entire arch 5 and foon after, the beams of the fun 
being very ilrong, there appeared a fecondary /m, whofe 
colours were more than ordinary bright, but inverted as ufu- 
allyj that is, the red was inwards, which in the primary Iris 
is outwards, and e contra for the blues ; but what appeared molt 
obfervable was, that with thefe two concentric arches, there 
appeared a third arch, nearly as bright as the fecondary /m, 
but coloured in the order of the primary, which took its rife 
from the interfc£lion of the horizon and prirnary /m, and 
went a crofs the fpace between the two, and interfe61:ed the 
fecondary, as in Fig. i. Plate IX. AFCG interfeas the 
fecondary Iris EFGD, dividing the arch ED nearly into 
three equal parts 5 but at firfl the arch A F did not appear, 
Vor.. HI. M m which 
