1876.] 



Observations made at Stonyhurst College. 



315 



present paper contains a precisely similar, and therefore comparable, reduc- 

 tion for the following six years of all the elements of terrestrial magnetism. 

 In the former paper the general result was somewhat at variance with the 

 conclusions arrived at by Sir Edward Sabine from a discussion of the 

 Kew observations ; and hence the necessity for this second paper, to dis- 

 cover whether local influences or mere accidental errors would account 

 for the discrepancies. The change of the station of observation during 

 the period from 1863 to 1870 introduced a probable source of error into 

 the first Stonyhiirst series ; but that uncertainty is now removed, as all 

 the obsen ations since 1868 have been taken in the fixed magnetic hut. 

 It will be unnecessary here to repeat what was said in [the former paper 

 on the subject of the instruments used in the observations, as these have 

 remained unchanged since 1863. The only alteration in the observations 

 themselves has been the substitution of weekly in heu of monthly read- 

 ings of the DecHnation from the beginning of the year 1872. 



Tlie Horizontal Force. 



Table I.— Monthly mean values of the Horizontal Force. 



Summer 

 Months. 



1870. 



1871. 



1872. 



1873. 



1874. 



1875. 



Mean 

 of six 

















years. 





3-6151 



3-6354 



3-6275 



• 3-6305 



3-6388 



3-6459 



3-6322 



May 



3-6164 



3-6242 



3-6290 



3-6353 



3-6400 



3-6481 



3-6322 





3-6256 



3-6250 



3-6262 



3-6314 



3-6390 



3-6418 



3-6315 



July 



3-6273 



3-6211 



3-6309 



3-6303 



3-6377 



3-6399 



3-6312 





3-6229 



3-6218 



3-6298 



3-6333 



3-6425 



3-6442 



3-6324 





3-6009 



3-6370 



3-6297 



3-6311 



[3-6446] 



3-6524 



3-6326 





3-6180 



3-6276 



3-6289 



3-6320 



3-6404 



3-6454 



3-6321 





Winter 

 Months. 



1870-71. 



1871-72. 



1872-73. 



1873-74. 



1874-75. 



1875-76. 



Mean 

 of six 















years. 





3-6207 



3-6249 



3-6341 



3-6366 



3-6466 



3-6448 



3-6346 





3-6183 



3-6303 



3-6356 



3-6298 



3-6468 



3-6492 



3-6350 





3-6249 



3-6340 



3-6401 



3-6351 



[3-6480] 



3-6504 



3-6388 





3-6256 



3-6300 



3-6289 



3-6466 



3-6492 



3-6485 



3-6381 





3-6207 



3-6328 



3-6330 



3-6410 



3-6447 



3-6482 



3-6367 





3-6229 



3-6321 



3-6218 



3-6412 



3-6414 



3-6443 



3-6340 



Means 



3-6222 



3-6307 



3-6323 



3-6384 



3-6461 



3-6476 



3-6362 



Yearly means . . . 



3-6201 



3-6292 



3-6306 



3-6352 



3-6433 



3-6465 



3-6342 



The figures for September and December 1874 are interpolations. 



