MAGNETIC SURVEY OF GREAT BRITAIN. 



147 



If we combine the mean results at the twenty-four stations 

 in this table by the method of least squares, we obtain the fol- 

 lowing values : a: =+ -000061 ; ^=--000066; M=-47° 37'; 

 r='000090; andy= 1*0136, at the mean geographical position 

 in lat. 53° 49', and long. 2° 08'. 



Mr. Fox's observations. — These were made with a 4| inch 

 needle, on the principle described by its maker, Mr. T. B. 

 Jordan, of Falmouth, in the third volume of the " Annals of 

 Electricity," &c. The needle has a small grooved wheel on its 

 axle, which receives a thread of unspun silk, furnished with 

 hooks, to which weights may be attached. The weights em- 

 ployed were successively 2*0 grains, 2' 1 grains, 2'2 grains ; and 

 with each weight the intensities are in the inverse ratio of the 

 angle of deflection produced, corrections being applied for 

 differences of temperature at the different stations. The fol- 

 lowing table exhibits the angles of deflection occasioned by 

 the respective weights, and the values of the intensity deduced 

 therefrom. The angles are reduced to a common temperature ; 

 1° of the centigrade scale having been found by experiment to 

 be equivalent to 2', or 2'*4 in the angle. 



Table XLVIII. 



Weight. 



Angle of 

 Deflection 



Intensity. 



Place of 

 Observation. 



I London 



Eastbourne 



Eastwick Park ... 



Combe House ..., 



Falmouth 



1838. 

 May 22 

 June 4 & 8 



June 20 



June 16 



July 2 



July 5 & 7 



Grains. 

 f2-0 

 \2-l 

 [2-2 



20 

 21 

 2-2 



'20 

 21 

 2-2 



20 

 21 

 22 



■20 

 21 

 2-2 



48 367 



51 55-3 

 55 330 



48 57 



52 19 

 55 57 



48 35 



51 57 



55 40 



48 25 



51 45 



55 18 



48 29 



51 48 



55 20 



1-0000 

 1-0000 

 1-0000 



0-9938 

 0-9921 

 0-9952 



0-9997 

 0-9996 

 0-9986 



1-0023 

 1-0024 

 I-003I 



10013 

 1-0017 

 1-0026 



1.0000 



.0-9937 



} 



0-9993 



1-0026 



-1-0018 



f Mean of results in 

 a field N. of Mai. 

 J den Lane ; in the 

 "S Regent's Park ; 

 and at West- 

 I t)ourne Green. 



{In the grounds 

 of Davies Gil- 

 bert, Esq. 



In the grounds. 



In the grounds. 



In Mr. Fox'i 

 grounds. 



