56 
Transactions of the Royal Society of South Africa. 
In the table below, column 1 indicates the hours and column 2 the 
mean hourly velocities for those hours for the 180 lunations = (5135 lunar 
days) from April, 1897, to October, 1911. There were two gaps in the 
period, when the anemometer had to be dismounted for repairs — one, from 
September 24 to October 8, 1908, being filled up from values obtained 
during September 26 to October 10, 1916 ; the other, from July 9 .to 23, 1911, 
being filled up from values obtained during July 13 to 27, 1916. 
According to column 2, the curve purporting to show the lunar effect on 
the velocity of the wind has only one definite maximum and minimum, the 
former falling about three hours before lunar midnight, the latter about an 
hour before lunar noon, the range being "20 miles an hour. 
Column 3 shows the result for the 2538 days of the period when the 
moon was south of the equator, and column 4 the result for the 2597 days 
when the moon was north. 
The general inference from column 3 is a maximum velocity near lunar 
noon and a minimum near midnight, with a range of "32 miles an hour ; 
whereas column 4 gives almost exactly the opposite tendency with a range 
of '55 miles an hour. These ranges are considerably greater than one would 
have expected to find. The lesser range for the time when the moon is 
south is probably partly due to the small secondary minimum shown in 
column 3 at lunar noon. 
If the variations of velocity shown in the table are to be regarded 
as entirely due to the lunar atmospheric tide, it is not easy to explain 
why column 2 shows only one maximum and minimum in the lunar day, 
especially as a preliminary investigation of the variations of velocity at 
perigee suggests a strong semidiurnal oscillation, with maxima at lunar 
moon and midnight, and minima near moonrise and moonset. This point, 
however, is reserved for treatment at some later time. Meanwhile it 
is easy to see that if, when the moon is in north declination, there is 
only one maximum of velocity in the lunar day, and that synchronising 
with the lower meridian passage, there should be, when the moon is in 
south declination, only one maximum, and that synchronising with the 
upper meridian passage. For the maximum aerotidal effect of the moon's 
action is felt in the southern hemisphere near the antipodes of the sub- 
lunar point when the moon is in the north, and near the sub-lunar point 
itself when the moon is in the south. In this connection it is worth notice 
that when the moon's declination, north or south, is greatest, the semi- 
diurnal lunar atmospheric tide at Kimberley practically disappears, resolving 
itself into a single oscillation, the phase when the moon is north being 
nearly the reverse of that when the moon is south.* 
The results given in this paper throw no light apparently on the possible 
* Corresponding to this diurnal inequality there are indications of an atmospheric 
swell following the moon to and fro across the equator. 
