398 Scientific Proceedings, Royal Dublin Society. 
These lead to the normal equations — 
10:°257+ 3858:25y=—- 1087-5, 
309°204 + 19592°25y = — 42197°5, 
from which we obtain the following solution :— 
Weight. 
e#=— 172452 + 36°4 3°9 
y=- 064+ 0°53 | 7420-0; 
while the probable error of a single observation is + 72°. 
We thus get for the period of rotation of the spot— 
95 55™ 33-36 + 05-53, 
and the epoch from which to reckon the rotations— 
February 9th, 8" 11™ 3158. 
It will thus be seen that this spot is moving at about the 
average velocity of the zone in which it lies; and it is interesting 
to note that this period agrees within one-fifth of a second with 
the value deduced by Schroeter 109 years ago from 242 revolu- 
tions of a spot, a fact which goes to show that there has been no 
permanent change in the period of rotation of this region in the 
interval which has elapsed since then. 
