Report of the Kew Committee. 



129 



APPENDIX I. 



Magnetic Observations made at the Kew Observatory, Lat. 51° 28' 6" N., 

 Long. O h l m 15 s ! W., for the year October 1879 to September 1880. 



The observations of Deflection and Vibration given in the annexed 

 Tables were all made with the Collimator Magnet marked K C 1, and 

 the Kew 9 -inch Unifilar Magnetometer by Jones. 



The Declination observations have also been made with the same 

 Magnetometer, Collimator Magnets N D and N E being employed for 

 the purpose. 



The Dip observations were made with Dip-circle Barrow No. 33, the 

 needles 1 and 2 only being used ; these are 3-J- inches in length. 



The results of the observations of Deflection and Vibration give the 

 values of the Horizontal Force, which, being combined with the Dip 

 observations, furnish the Vertical and Total Forces. 



These are expressed in both English and metrical scales — the unit in 

 the first being one foot, one second of mean solar time, and one grain ; 

 and in the other one millimetre, one second of time, and one milligramme, 

 the factor for reducing the English to metric values being 0*46108. 



By request, the corresponding values in C.G.S. measure are also given. 



The value of log 7r 3 K employed in the reduction is 1*643G5 at tem- 

 perature 60° F. 



The induction-coefficient ja is 0*000194. 



The correction of the magnetic power for temperature t to an 

 adopted standard temperature of 35° F. is 



0*0001194(£ o -35)+0*000,000,213(£ o -35) 3 , 



The true distances between the centres of the deflecting and deflected 

 magnets, when the former is placed at the divisions of the deflection- 

 bar marked 1*0 foot and 1*3 feet, are 1*000075 feet and 1*300097 feet 

 respectively. 



The times of vibration given in the Table are each derived from the 

 mean of 12 or 14 observations of the time occupied by the magnet in 

 making 100 vibrations, corrections being applied for the torsion-force 

 of the suspension-thread subsequently. 



No corrections have been made for rate of chronometer or arc of 

 vibration, these being always very small. 



The value of the constant P, employed in the formula of reduction 



1-— \ is -0*00109. 



r V 



In each observation of absolute Declination the instrumental read- 

 ings have been referred to marks made upon the stone obelisk erected 

 1,250 feet north of the Observatory as a meridian mark, the orientation 

 of which, with respect to the Magnetometer, was determined by the 

 late Mr. Welsh, and has since been carefully verified. 



The observations have all been made and reduced by Mr. F. Gr. Figg. 



m ( 



