cs 
ares it does not set till midnight, and Sais shines iueuphouttia period 
- dn brightness and the maximum effect in extinguis 098 faint aurore 
142 Miscellaneous Intelligence. 
that till some better mode of measuring this intensity can be devised for 
these high latitudes, we are forced to perform this operation in a rude 
manner, by moving to lower latitudes, where the fainter aurore be- 
come invisible, and. ae therefore, frequency is a test of intensity 
beyond a certain limit. 
Combining the numbers of aurorz observed at each day of the moon’s _ 
age into six groups of five days, (the first group, four and a-half days,) 
we find the average number of aurore for one day of the moon’s age 
in each group as follows, from the six and a-half years’ observations : 
Moon’s age, 28d—2d 3d—7d 8d—12d 13d—17d 18d—22d 23d—27d 
Number SGins THs. SG 50 10:2 6°6 
Did aurore occur indifferently at all ages of the moon, we should 
expect to see the greatest number at conjunction, and the least number 
m 
and minimum occurred at times equidistant from the woe of oe 
The frequency of aurore, therefore, is a runes) of the moon’s age. 
i aw, we consider the probable 
effect of moonlight in obliterating the staal aphes rances ; remarking, 
first, that 9h p.m. is the epoch of maximum frequency for the aurora, 
the occurrence of five-sixt ka of the aurore: afterwards it increases 
is evidently attained at opposition, when the egins’ to ‘rise late 
enough to allow the earlier aurorze to be visible ; varie the end of the 
third quarter when the moon does not rise till midnight, it is also evident 
that the number of faint aurore rendered invisible must e very small. 
From the beginning of the fourth quarter, therefore, - sr idpprsi® the 
numbers seen will obey nearly the true law of frequency ; and as 
visible maximum occurred before the end of the third se tape the true 
maximum must have occurred even nearer to opposition. On the whole, 
it appears very certain, that the hypothesis of an actual pide of 
frequency at opposition, and minimum at con gis es is satisfied by the 
previous numbers of aurore seen under the conditions of the varying 
duration of mgootgnt the hours of maximum free Sack This hy- 
pothesis is in unison the pe of magnetic sarge which is @ 
maximum at oppos ibs, and a minimum at conjun 
4. Relative level of the Red “ike and Medi escee ;.(Lilnstitut, 
No. 874.)—The following measurements are by the engineers.attached 
to the Expedition to Egypt in 1799, and by Bourdaloue —— in Loe 
with cxep ning ‘and levelling across the isthmus. 
Expedition. Bourdaloue. : 
Ser water ‘et Tineh, -0-00 0™-00- 
aptigh water at Suez, 9 - a: 2a 
90 
water on the Nile at Mekias, 5 -29 13 27 
; 
Ra ae 
eka. E 
so = hid ine ln 
oie) ee 
