MADE AT STONYIIURST COLLEGE OBSERVATORY. 73 
is =0'00025, has led us into no sensible error, but that the corrections applied for the 
change of station between July 18G4 and March 1868 should be somewhat modified. 
Table III. gives as the probable error of a single observation, or monthly mean, 
MzO’00332, and neglecting January 1868, + 0-00292; and for the error of the mean 
+000036, or neglecting January 1868, +0-00032. 
The Dip Observations may now be treated in a precisely similar manner as those of 
the Horizontal Force. 
Table I. 
Monthly mean values of the Dip. 
April to September. 
1S63. 
1864. 
1865. 
1866. 
1867. 
1868. 
1869. 
Mean. 
April 
69 51 13 
46 29 
49 57 
48 52 
45 17 
40 45 
43 57 
69 46 39 
May 
48 37 
46 40 
50 42 
47 26 
44 16 
41 9 
37 34 
45 12 
June 
47 50 
49 15 
49 21 
47 33 
43 22 
39 57 
38 45 
45 9 
July 
51 27 
47 44 
50 29 
48 32 
47 24 
42 11 
38 9 
46 34 
August 
49 51 
47 29 
51 8 
46 19 
46 15 
36 58 
40 49 
45 33 
September 
48 15 
50 35 
50 0 
46 11 
45 16 
40 45 
35 15 
45 11 
Means 
69 49 32 
O* 
00 
50 16 
47 29 
OO 
40 18 
39 5 
69 45 43 
October to March. 
1863-64. 
1864-65. 
1865-66. 
1866-67. 
1867-68. 
1868-69. 
1869-70. 
October 
69 48 23 
48 20 
51 4 
47 15 
43 33 
43 4 
35 1 6 
69 45 16 
November 
48 30 
49 22 
48 39 
46 33 
44 34 
42 23 
39 52 
45 42 
December 
47 17 
49 57 
47 5 
46 45 
43 0 
41 52 
36 3 
44 34 
January 
47 21 
47 15 
47 21 
46 53 
43 40 
42 34 
33 16 
44 3 
February 
49 13 
50 4 
49 37 
45 19 
45 8 
40 7 
36 16 
45 6 
March 
47 19 
49 17 
50 3 
46 16 
43 50 
40 43 
39 6 
45 13 
Means 
69 48 1 
49 3 
48 58 
46 30 
43 58 
41 47 
36 38 
44 59 
Yearly means 
69 48 47 
48 32 
49 37 
•<r 
o 
44 38 
41 2 
37 52 
69 45 21 
The values for August and October 1863 are interpolated. 
The mean dip for October 1st, 1866, is thus 69° 45' 21". 
With a secular diminution =1' 49"*2. 
From these quantities we will now calculate the semiannual inequalities. 
