238 Dr. B. Stewart on Observations of Dip [Mar. 3, 



ferences determined by this process) ±0 I 'S7 ) instead of + 0 f, 96, which it 



was before. 



II. Horizontal Force. 

 13. In Table VI. we have a record of the observed values of horizontal 

 force made with the Kew unifilar by Mr. Whipple, each observation being 

 made and reduced precisely after the manner of those described by Sir E. 

 Sabine in his analysis of the first six yearly series. 



Table VI. 



Monthly values of the Horizontal Component of the Earth's Magnetic 

 * Force at Kew, calculated from the results of observations of deflection 

 and vibration with Collimator Magnet K.C.I. 



May 



June 



1863. 



1864. 



1865. 



1866. 



1867. 



1868. 



Mean of 

 6 years. 



3*8201 



3-8I99 

 3-8198 

 3-8260 



3- 82 43 

 3-8205 



3-8240 

 3-8260 

 3-8246 



3-8331 

 3-8264 



3-8314 



3-8277 

 3-8251 

 3-8258 

 3-8330 

 3-8246 

 3-8298 



3*8338 

 3-8373 

 3-8383 

 3-8410 



3-8384 

 3-8386 



3-8449 

 3-8459 

 3-8469 



3-8427 

 3'8445 

 3-8467 



3-8464 

 3-8504 

 3-8495 

 3-84H 

 3-8511 

 3-8476 



3-8328 

 3-834I 

 3*8341 

 3-8362 

 3-8349 

 3-8358 





3-8218 



3-8276 



3-8277 



3*8379 



3-8453 



3-8477 



38346 





1863-64. 



1864-65. 



1865-66. 



1866-67. 1867-68. 



1868-69. 



Mean of 

 6 years. 



February 



3-8142 

 3-8214 

 3-8218 

 3-8239 

 3-8242 

 3-8229 



3-8274 



3'8243 

 38293 

 3-8276 

 3 8353 

 3-83'9 



3-8271 



3-8325 

 3-8360 



3-8364 

 3-8335 

 3-8357 



3-8354 

 3-8410 

 38396 

 3-8443 

 3-84 0 5 

 3-8403 



3-8446 

 3-8494 

 3-8475 

 3-8511 



3-8492 

 3-8469 



3-8470 

 3-8503 

 3-8539 

 [3-8521] 

 3*8504 

 3-8521 



3-8326 

 38365 

 3*8380 

 3'8392 

 3-8388 

 3-8383 





3-8214 



3-8293 



3/8335 



3-8402 



3-8481 



3-8510 



3-8372 





3-8216 



3-8284 



3-8306 



3-8391 



3-8467 



3-8493 



3-8360 



The value within brackets is interpolated. 



14. The absolute values of the horizontal force corresponding to the 

 beginning of October in each of the years comprehended in the above 

 Table, and the secular change in each year are as follows : — 



From April 1863 to March 1864 3 8216 1 , , . . 



x J v secular change + o 0068 



„ 1864 „ „ 1865 3-8284^ 



L „ „ +0-0022 



„ 1865 „ „ ' 1866 3-8306 J 



\ n » +0-0085 



„ 1866 „ „ 1867 3-8391 \ 



\ ft n +0*0076 



„ „ 1867,, „ 1868 3-8467 \ 



\ „ » +0-0026 



„ 1868 „ „ 1869 3-8493 J 



Mean of the six years corresponding to 1 >% f, J With a mean annual sccu- 



middle epoch, April 1, 1866 J 3 3 °\ lar increase of o - oo 55. 



