70 
Transactions of the Boyal Society of South Africa. 
Jan. 28 at 7.20 p.m., height of water-level 1-37 in. above datum 
7.45 p.m. „ 1-47 
9.10 p.m. „ 1-67 
10.10 p.m. „ 1-75 
11.5 p.m. „ 1-97 
29 12.10 a.m. „ 2-12 
1.15 a.m „ 2-12 
I. 45 a.m. „ 2-25 
2.25 a.m. „ 2-00 
9.45 a.m. „ 0-81 
10.0 a.m. ,, 1-00 
10.10 a.m. „ 1-19 
10.25 a.m. „ 1-37 
10.40 a.m. „ 1-50 
10.50 a.m. „ 1-69 
II. 4 a.m. „ 1-56 
11.20 a.m. „ 1-75 
11.33 a.m. „ 2-00 
11.53 a.m. „ 2-06 
12.6 p.m. „ 2-12 
12.25 p.m. „ 2-19 
12.40 p.m. „ 2-25 
12.55 p.m. „ 2-44 
1.10 p.m. „ 2-37 
1.25 p.m. „ 2-44 
2.30 p.m. „ 2-50 
3.40 p.m. „ 2-37 
5.55 p.m. ,, 1-56 
30 9.30 a.m. „ 0-19 
9.45 a.m. „ 0-22 
10.30 a.m. „ 0*75 
The highest part of the inner edge of the exit pipe was 0*31 in. below 
the datum line. 
The curve obtained by plotting these measurements on squared paper 
like the curve of the yield shows a maximum on January 28 in the neigh- 
bourhood of 1 p.m. and a minimum about 6 p.m. 
Further, it may be said to show in a general way in the course of a 
day and a half three maxima and three minima at roughly equal intervals 
of six or seven hours. 
It was now apparent that the best means of obtaining further infor- 
mation about the periodic variation of yield would be some form of clock- 
driven, self-recording instrument registering the fluctuations of water-level 
