2 
RAINFALL OF SOUTHERN RIVERINA. 497* 
(IV.) Summary.—In dealing with a subject so uncertain as 
rainfall, the most important feature to be discovered is its 
periodicity. In fact I think that this is the only point of impor- 
tance in connection therewith. 
The question of periodicity has been dealt with by many writers, 
and the number of different theories advanced is somewhat per- 
plexing. There are periods of three, five, eleven, nineteen and 
thirty-three years ; all of these have their supporters. In many 
instances an agreement exists between one of these periods and 
the figures representing the rainfall, and this agreement is im- 
mediately set forth as a positive theory. As it is orthodox to 
assume that rainfall is governed by certain laws, more or less 
proven, argument on the matter is out of place in these notes. 
Suffice it to say that I do not consider that the records of twenty- 
three years which I have now set before you, show definitely any 
periodicity, for the simple reason that T do not think the observa- 
tions cover a sufficiently long series of years to actually prove 
anything. I beg to draw your attention though to the fact that 
the amounts of the annual totals coincide closely and conform to 
the period set down as a nineteen year cycle. By taking the 
monthly values I find that the period shows eighteen years two 
months. For instance, the dry period commencing in October 
1874, and lasting for four months is repeated in December 1892, 
when a dry period of three months set in. 
The annual results agreeably conform to the nineteen year 
cyele as shown by the following examples :—1875, 1894, and the 
three years immediately preceding these years respectively. These 
oe what may be called all good years or years of a plentiful 
rainfall, Unfortunately our series for this district does not give 
us an opportunity of comparing the recurrence of the dry years. 
viegne Tam correct in stating that the nineteen year period 
Fig = our Government Astronomer Mr. H. C. Russell, 
mention this to show the excellence of the authority i 
quote when applying the cycle to this discussion. 
Fr—Deec. 4, 1995. 
