SS2 



riGURE OF THE KARTH. 



Bat, if we attend to the angular dimensions of the several 

 arcs^ as dedncod from observations and from calculation, these 

 will not be found to agree so nearly. 



The following table will shew the differences in each instance. 



But in dcg.and 

 pts they differ 

 ▼cry consider- 

 »Wy. 



Clifton and Dunnose 



Difference 



2° 50' 23 ",35 observed 

 2 50 21 ,97 calculated 



+ 1 ,38 



Clifton and Arbury 

 Difference 



f 1° U' 3", 

 t ] 13 58 ,( 



1° 14' 3",40 observed 

 ,63 calculated 



+ 4 ,1^ 



Arbury and Dunnose / 



36 



19' .j95 observed 

 23 ,34 calculated 



Difference 



-3 ,39 



toises in a 

 degree. 



The excess of 

 the total arc is, 

 Jiovvever,inuch 

 less 



Hence the ap- 

 parent increase 

 in the degs. is 

 to be ascribed 

 to error of obs. 

 ef Tat. at Arbu- 

 ry HiU. 



These differences are really considerable, and are capable 

 of producing important errors in the recults dependent on them. 



In the first place we see, that the southernmost arc between 

 Dunnose and Arbury is smaller than it would appear by com- 

 putation, i)y as much as 3",4, and when this deficiency is 

 combined with an excesi of 8 toises in the linear dimensions 

 of the same arc, it makes as much as 40 toises difference in 

 the estimated length of a degree. The reverse of this occurs 

 in the northern portion of the arc comprised between Clifton 

 and Arbury Hill. This is larger than it ought to be by 4",77, 

 and hence the value of a degree on the meridian turns out too 

 small by about 62 toises in its linear dimensions. Fortunately 

 however, the excess of the total arc is extremely small, as it 

 does not exceed T ,38, so as to make but 5 or 6 toises differ- 

 ence in the length of a degree observed on the meridian, and 

 xorresponding to the mean latitude of the arc examined. 



From what has been above stated, it seems almost beyond a 

 doubt that it is to errors in the observations of latitude, that the 

 appearance of progressive augmentation of degress towards the 

 equator, as represented by Lieut. Col. Mudge in his paper, are 

 to be ascribed, and that it is especially at the intermediate sta- 

 tion 



