158 
SIK NORMAN LOCKYER AND OTHER8 UN THE 
order that there might be no mistake about the calls, a spiral was drawn on the clock- 
face and the seconds left plainly marked at the points which the second hand would 
occupy during its two revolutions (fig. 2). The time calls were repeated by two 
assistants, who stood about 50 yards from the eclipse clock, for the benefit of the 
observers in the outlying parts of the camp. 
For the work of the prismatic cameras it was important to get a signal as nearly as 
possible 5 seconds before the beginning of totality, and, in oi’der to eliminate the 
possilfie error of the chronometer, it w^as arranged to determine this by direct obser¬ 
vations. Two methods were adopted. In one of them a boat was moored at a 
distance of 2 miles from the camp, in the direction of approach of the shadow, which 
Avoidd pass this point 5 seconds before totality. This failed because of the indefinite 
boundary of the shadow. 
The other method was to determine when the visible remaining crescent subtended 
an angle of 45° ; calcidation showed that this would occur at the desired interval 
from totality. This method was completely siiccessful. 
A signal at 25 seconds before commencement of totalitv was also civen from obser- 
vatlons, the cusps then subtending an angle of 90°. These observations of the cusps 
were made by Lieutenant de Wet. 
The chronometer was 5h. 8m. 35'Ss. slow on mean time at Yiziadrug, and 
Oh. 15m. 20s. slow on Greenwich mean time, as determined by Lieutenant Qu ayle. 
