70 



EIGHTH REPORT 1838. 



Table XII. contains the latitudes and longitudes of Mr. 

 Lloyd's stations, and the mean dip at each station : the number 

 of distinct comparisons are, at London *2, Shrewsbury 2, 

 Ryde 2 ; at each of the other places, 1 : in the subsequent 

 calculation, these numbers are taken as the weights. 



Table XII. 



If we combine these fourteen results by the method of least 

 squares, we obtain the following values : a; — + -2899 • 

 y=--5753; «=-63°15'; ?- = 0-644 ; and S = 69° 54' at the 

 mean geographical position, of which the latitude is 52° 4', and 

 the longitude 1° 43' W. 



Professor Phillips's Observations.— These were made with a 

 six-inch circle and two needles, by Robinson. At some of the 

 stations marked f, the reversal of the poles was intentionally 

 omitted, from a desire to determine small local differences, under 

 circumstances as similar as possible, the needles being very 

 nearly equilibrated. The table shows which of the observations 

 were thus incomplete ; and the comparison of the results at the 

 other stations, before and after the reversal of the poles, shows 

 the probable small limit of error which may have been involved 

 by the omission. With the poles direct, and also with the poles 

 reversed, the mean of four positions was taken, being eight in all ; 

 the needle was always inverted on its supports, as well as the 

 circle turned in azimuth : four readings of each end of the 

 needle were generally taken in each position. 



