MADE AT STONYHURST COLLEGE OBSERVATORY. 
71 
The Horizontal Force. 
Table I. 
Monthly mean values of the Horizontal Force. 
April to September. 
1863. 
1864. 
1865. 
1866. 
1867. 
1868. 
1869. 
Mean of 
seven years. 
April 
May 
June 
July 
August 
September 
3-5912 
3-5920 
3-5850 
3-5988 
3-5956 
3-5924 
3-5950 
3-5995 
3-5999 
3-6004 
3-5924 
3-5876 
3-5958 
3-6016 
3-5997 
3-5920 
3-5987 
3-5996 
3-5978 
3-5985 
3-6004 
3-6063 
3-5980 
3-5973 
3-6094 
3-6088 
3-6090 
3-6070 
3-6104 
3-6067 
3-6052 
3-6099 
3-6100 
3-6055 
3-6060 
3-6129 
3-6157 
3-6250 
3-6195 
3-6138 
3-6177 
3-6077 
3-6014 
3-6050 
3-6034 
3-6034 
3-6027 
3-6006 
Means 
3-5925 
3-5958 
3-5979 
3-5997 
3-60S5 
3-6083 
3-6166 
3-6028 
October to March . 
1863-64. 
1864-65. 
1865-66. 
1866-67. 
1867-68. 
1S68-69. j 1869-70. 
October 
November 
December 
January 
February 
March 
3-5909 
3-5894 
3-5962 
3-5944 
3-5971 
3-5877 
3-5891 
3-5953 
3-5912 
3-5959 
3-6001 
3-5969 
3-5912 
3-5966 
3-5978 
3-5986 
3-5990 
3-5958 
3-5992 
3-6036 
3-6036 
3-6043 
3-6061 
3-6060 
3-6101 
3-6079 
3-6073 
3-5871 
3-6060 
3-6066 
3-6173 
3-6173 
3-6194 
3-6194 
3-6223 
3-6100 
3-6190 
3-6204 
3-6249 
3-6236 
3-6166 
3-6099 
3-6024 
3-6044 
3-6058 
3-6033 
3-6067 
3-6018 
Means 
3-5926 
3-5948 
3-5965 
3-6038 
3-6042 
3-6176 
3-6191 
3-6041 
Yearly means 
3-5926 
1 
3-5953 
3-5972 
3-6018 
3-6064 
3-6129 
3-6178 
3-6034 
The values for August and October 1863 are interpolations. 
The value in January 1868 is evidently too small ; this arose from a sudden change 
in the time of vibration of the magnet. 
The above Table gives for the epoch October 1st, 1866, 
The mean Horizontal Force =3‘6034. 
With a secular acceleration =0-0042. 
These quantities enable us directly to calculate the probable value of the force at any 
epoch, and we thus form the next Table. 
L 
9 
