171 



disturbed with reference to its sides ; and, this needle with its 

 weight, can be conveniently employed to determine both dip 

 and intensity by the same observations. 



By Dr. Lloyd's method I found the following comparative 

 data for York and London in February and March, 1838. 

 6 is the angle by which the needle deviates from the horizontal, 

 when suspended in the magnetic meridian. 



Temp. 9 S 



1838, Feb. 19, York 33- ... — 16° „ 54 -87 ^ 



>• 70° „ 48 '8 

 38- ... —16 55 -23 



Mar. 28, London 58- ... —-19 22 '2 69 19 '6 



From which by the formula -^^^ and a small correction 

 for temperature, we have 



Intensity at London 1*0000 



„ at York 1*0126 



Again in 1850 1*0128 



By Professor Christie's method, which requires calculations 

 reducible to the same form as Dr. Lloyd's, I found the inten- 

 sities at York and London — in 1837, 1838, and 1850. 



1837, 1*0125 to 10000 



1838, 1*0075 

 1850, 1*0089 



Mean ... 1*0093 



If we now collect all these results in one point of view we 

 find the ratio of the intensity at York to that in London. 



Mean. 

 By Vibrations 1*0149 



} 



By Lloyd's Needle 1*0126 ... 1838 



, ^, . 1838 ... 1*0121 

 1*0094 



. 1*0127 

 1*0128 ... 1850 



By Christie's Needle 1*0115 ... 1837 



1*0075 ... 1838 > 1*0093 



1*0098 ... 185( 



} 



38 > 

 50 3 



General mean 1*0114 



