Lieut. Foster's corrections 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 182 6. 
Table VII. page 220, Philosophical Transactions, Part IV. 1826. 
srvations for determining the apparent altitude of Arcturus at the time of setting, by 
Lieutenant Foster’s upper telescope. 
esponding 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. 
At io h A. M. 
11 A. M. 
10 A. M. 
( 9 A. M. 
i to 
( iJP.M. 
io A. M. 
16 
12 
12 
6 
6 
6 
1 6 
O / // 
238 34 17,5 
147 3 i 2,5 
56 28 2,5 
1 9 ° 55 57,5 
325 23 57,5 
99 52 6,25 
238 34 10,25 
// 
+ IO 
0,0 
/ n 
+ 3 13,47 
+ 1 13,57 
+0 49,05 
+0 54,50 
+0 10,90 
+0 2,72 
+ 2 38,05 
O / // 
7 35 8,69 
7 35 I0 , IZ 
7 35 10 , 9 2 
7 35 n ,75 
7 35 i7,*8 
7 35 i8 ,°9 
7 35 ",98 
Inches. 
29,540 
29,610 
29,626 
j 29,460 
29,600 
O 
26 
—29 
—35 
—40 
—36 
— 3 i 
ESE U. 
Easterly 
Calm 
Calm 
Calm 
Fine and Clear. 
Hazy, with slig 
Clear and Fine 
Weather. 
Clear and Fine. 
hit Snow. 
Thin haze near 
the horizon. 
Hazy near the 
horizon. 
Mean to be used in Table VIII. 7 35 12,68 instead of 7 35 18,43 
Micrometrical Measure as before + 1 49,82 
Altitude to be used in Table IX. zz 7 37 2,50 instead of 7 37 8,14 
principal vernier was not reset to zero after the observations on the 1 8th, but the readings were continued in the 
observations, except on March 4th, when the principal vernier was reset to zero. 
