202 
The equations formed from these data, treated by the 
method of least squares, give ; 
Mean Epoch — 1869, January 23 •89. 
Mean Period=14G*527 days. 
The mean of the two values of the period is 146‘599 days, 
and using this to calculate the times of minima and maxima, 
we have the following differences between the calculated 
and obsei'ved times of minimum : — 
Days. Days. 
5-6 
... - 8-4 
— 
6-2 
... - 0-2 
+ 
0-6 
... +11-4 
4 - 
10*8 
... -13*4 
+ 
0.4 
The average difference is 6*3 days, or about 2 V of the 
whole period. 
The differences between the calculated and observed 
times of maxima are 
Days. 
Days. 
+ 12-1 
+ 7-1 
+ 2-3 
+15-3 
-15-5 
- 2-7 
-13-9 
+ 4-1 
- 8.7 
The average difference is 9’1 days, or about of the 
whole period. The irregularities in the times of maximum 
are thei’efore greater than in those of minimum. The dis- 
tribution of the plus and minus differences in the two 
series of results does not seem to indicate that any sensible 
change has taken place in the length of the period. 
Like many other variables, T Aquilse increases in bright- 
ness more rapidly than it diminishes, the mean interval from 
minimum to maximum being 68’5 days, and from maximum 
to minimum 78*1 days. 
The mean magnitude at minimum is 11*08; the lowest 
minimum yet observed is 11-6, and the highest 10-7, thus 
