Lieut. Foster’s correctmis to the reductions^ &c. 123 
circle in question, I was given to understand that the value of 
each division of the* level was equal to one second in arc :-~ 
and as this instrument was the same that had been employed 
by Captain Sabine, in his experiments on the pendulum, I 
took no steps to examine this point for myself, for it never 
once occurred to me that there could exist a doubt on the 
subject. 
The following, however, are the corrected Tables, which 
are similarly numbered with those they are intended to be 
substituted for, in pages 220 and 223 of Part IV. of the Phi¬ 
losophical Transactions, for 1826. 
Table VII. page 220, Philosophical Transactions, Part IV. 1826. 
ibservationS for determining the apparent altitude of Arcturus at the time of setting, by 
Lieutenant Foster’s upper telescope. 
corresponding observations for refraction are contained in Tables VIII. and IX. pages 221 and 222 in Part IV. for 1826. 
• 
Time. 
No. of Obs. 
Mean Reading of 
the Four Verniers. 
Corrections for 
Apparent 
Altitude. 
Barometer 
at Temp; 
4 - 48°. 
Temp. 
Fah.*^ 
Winds 
True. 
Weather, 
Remarks. 
Index. 
Level. 
th 
/ // 
0 / // 
Inches. 
0 
18 
At io’’A. M. 
16 
238 34 I 7 »S 
+ 10 
+ 3 i 3>47 
7 35 8,69 
29,540 
—26 
ESE L‘. 
Fine and Clear. 
19 
II A. M. 
12 
147 31 2,5 
— 
+ i 13.57 
7 35 50.12 
29,610 
—29 
Easterly 
Flazy, with slight Snow. 
20 
10 A. M. 
12 
56 28 2,5 
— 
+0 49,05 
7 35 10,92 
29,626 
—35 
Calm 
Clear and Fine 
Thin haze near 
C 9 A. M. 
6 
190 55 S 7>5 
— 
+ 0 54,50 
7 35 51.75 
'1 
—40 
Calm 
Weather. 
the horizon. 
21 
6 
325 23 576 
— 
4-0 10,90 
7 35 57.58 
> 29,460 
Hazy near the 
1 iJP. M. 
6 
99 52 6,25 
— 
+0 2,72 
7 35 58,09 
) 
—36 
horizon. 
4 
10 A. M. 
16 
238 34 10,25 
0,0 
+ 2 38,05 
7 35 15.98 
29,600 
—31 
Calm 
Clear and Fine. 
O / // 
Mean to be used in Table VIIL 7 35 12,68 instead of 7 35 18,43 
Micrometrical Measure as before + i 49,82 
Altitude to be used in Table IX. = 7 37 2,50 instead of 7 37 8,14 
The principal vernier was not reset to zero after the observations on the i8th, but the readings were continued in the 
[uent observations, except on March 4th, when the principal vernier was reset to zero. 
