126 Report S.A.A. Advancement of Science. 



hours of calm, 961 out of 1009, occurred in these periods. Besides 

 these rotations, I have noted about half-a-dozen clear movements from 

 East through South to South-West and back, or right round through 

 South in the course of a day. 



The veerings of the vane from E. or E.S.E. to N.E. or N. in 

 the middle of the day and back in the afternoon are not rare. The 

 behaviour of the barometer, thermometer, and hygrometer traces 

 induce me to think that they ought to be classed in the complete 

 rotation periods through North. 



The importance for us of these diurnal rotation periods comes 

 from the fact that over 80 per cent, of the rains in these two years fell 

 in this weather type. 



From January, 1904, to January, 1906, the rainfall has been 

 3i.6iins. distributed in the following way: — 



4.89ins. in the East wind periods. 



4.4iins. in the periods of East wind with several hours of N.E. or 



N. in the day. 

 2 1. 7 Bins, in the daily rotation periods. 



.53ins. on one rotation of the wind through South. 



This gives 70 per cent, for the veering wind periods alone, and 

 84 per cent, if we consider them with those in which there was a 

 notable amount of N. or N.E. wind. 



A more accurate discussion will very likely show that the amount 

 of rain due to the East wind periods is even less than 15 per cent., as 

 I find that a fair portion of the 4.89ins. fell in the passage from the 

 veering periods to the East wind periods, and ought to be considered 

 as part of the rains of the preceding day. 



There is a marked difference between the two sets of rains; the 

 east rains are mostly drizzles, amounting at the highest to one or 

 two-tenths of an inch in 24 hours. They are generally less than one- 

 tenth. Occasionally they turn into a slow, steady rain. On only one 

 occasion was there a record of more than one inch, i.28ins., in one of 

 the east wind periods, and most of this fell in the first day of it. 



The rains in the other periods are almost all heavy rains 

 connected with thunderstorms. Nearly all the thunderstorms noted in 

 the meteorological register are on days when the wind was veering, a 

 few on the days when N. or N.E. was very prominent, two on the first 

 day of some east wind periods. Thunder and lightning without storm 

 or rain occur very frequently, very rarely with pure east winds. Slow, 

 steady rains are rare with veering winds, and are almost always the 

 clearing rains after a thunderstorm. The fact that most of our rains 

 come from thunderstorms explains why they have a very local 

 character and why stations very little distant from one another and 

 in practically the same geographical position show rather marked 

 differences in the rain (v.g., Jan., 1906, rainfall at the Observatory 

 renins.; at the Waterworks, two miles away, 7.25ins.). 



This seems also to confirm the general idea that the Rhodesian 

 rains are due to the North and West winds. This question of the 

 origin of the rains in Rhodesia is not, however, easily settled. Mr. 



