756 Proceedings of the Royal Society 
1. When the prevailing wind has previously traversed a large 
extent of ocean, the rainfall is moderately large. 
2. If the winds are at the same time advancing into colder 
regions, the rainfall is largely increased ; and if a range of moun- 
tains lie across their onward path, the rainfall is also thereby 
largely increased on the side facing the prevailing winds, and 
reduced over the regions lying on the other side. 
3. If the winds, though arriving from the ocean, have not tra- 
versed a considerable extent of it, the rainfall is not large. 
4. If the winds, even though having traversed a considerable 
part of the ocean, yet on arriving at the land proceed into lower 
latitudes, or regions markedly warmer, the rainfall is small or nil. 
3. On the Lunar Diurnal Variation of Magnetic Declination 
at Tre van drum, near the Magnetic Equator. By J. A. 
Broun, F.R.S. 
The author gives the results derived from different discussions of 
nearly eighty thousand observations, made hourly during the eleven 
years 1854 to 1864. They are as follows : — 
1. That the lunar diurnal variation consists of a double maximum 
and minimum in each month of the year. 
2. That in December and January the maxima occur near the 
times of the moon’s upper and lower passages of the meridian ; 
while in June and July they occur six hours later, the minima 
then occurring near the times of the two passages. 
3. The change of the law for December and January to that for 
June and July does not happen, as in the case of the solar diurnal 
variations, by leaps in the course of a month (those of March and 
October), but more or less gradually for the different maxima and 
minima. 
4. While the lunar diurnal variation changes the hours of 
maxima and minima more gradually than the solar diurnal varia- 
tion, it also makes the greatest change at different times ; thus the 
solar diurnal variation changes completely during the month of 
March, or from February to April, while the lunar diurnal varia- 
tion makes the greatest change, from April to May. The second 
