470 



Report of the Kew Committee. 



APPENDIX I. 



Magnetic Observations made at the Kew Observatory, Lat. 51° 28' 6" N. t 

 Long. h l m 15 s -l W.,for the year October 1876 to September 1877. 



P The observations of Deflection and Vibration given in the annexed 

 Tables were all made with the Collimator Magnet marked KC1, and 

 the Kew 9-inch Unifilar Magnetometer by Jones, the property of the 

 Magnetic Office, directed by General Sir E. Sabine. 



The Declination observations have also been made with the same 

 Magnetometer, Collimator Magnet X E being employed for the purpose. 



The Dip observations were made with Dip-circle Xo. 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 Porce, which, being combined with the Dip 

 observations, furnish the Vertical and Total Eorces. 



These are expressed in both English and metrical scales — the units 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 values to metric value being 0-46108. 



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



The value of log 7r 2 K employed in the reduction is 1-64365 at tem- 

 perature 60°. 



The induction-coefficient fx is 0-000194. 



The correction of the magnetic power for temperature t to an adopted 

 standard temperature of 35° Eahr. is 



0-0001194(* -35) + 0'000,000,213(f -35) 2 . 



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 TO ft. and 1*3 ft., are 1-000075 ft. and 1-300097 ft. 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, emploved in the formula of reduction 



-=|;(l_l 2 ), is -0-00179. 



In each observation of absolute Declination the instrumental readings 

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

 a quarter of a mile north of the Observatory as a meridian mark, the 

 orientation of which, w T ith 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. P. G. Pigg. 



