30 On the Measurement of three Degrees of the Meridian. 



These last values exceed those resulting from my com- 

 putations, the first by 10 toises, the second by 2, the third 

 by 8 toises; and these diflerences arise from the conver- 

 gence ot the meridians, which the author thought might 

 safely be neglected, and in fact it does not make a difference 

 that is perceplible in the value of a degree upon the meri- 

 dian. For the difi'ercnce of S toises, in the distance be- 

 tween Dunnose and Arbury, makes but 5 toises difference 

 in the value of a degree upon that arc, and the difTerence 

 of 10 in the whole distance from Dunnose to Clifton, 

 makes 3| in the nieasure of each degree on that arc. So 

 liiat, as far as this source of disagreemeiit is concerned, the 

 author's results and mine would not be found to diflfer 

 materially from each other. 



But, if we attend to the aniT-ilar dimensions of the se- 

 veral arcs, as deduced from observation and from calcula- 

 tion, these will not be found to aoree so nearly. 



The following table will show the differences in each in- 

 stance. 



Clifton and Dunnose 



r 2^ 50' 23",35 observed 

 1 2 50 21 



!1 ,97 calculated 



Difference + 1 ,38 



rryr, , ., riM4' 3",40 observed 



C 1 ton and Arbury < , ,„ ,„ \,„ ■ i . i 



■' Li 13 38 ,b3 calculated 



Difference +4 ,77 



. , , y^ f 1° 36' 19", 95 observed 



Arburv and Dunnose i , „^ ^^ \,. i i . i 

 M 36 23 ,34 calculated 



Difference — 3 ,39 



Thoc differences are really considerable, and are capable of 

 P'foducing important errors in the resultsdepcndent on them. 

 In the lir>t place we see, that the southerniTiost arc be- 

 tween Dunnose and Arburv is smaller than it would ap- 

 pear by computation, by as much as 3''',4 ; and when this 

 deficiency is combined wit-h an excess 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. Tiie 

 reverse of this occurs in the northern portion of the arc 

 comprised between Clifton and Arbury Hiil. This is 

 larger than it ought to be by 4",77, and hence the value of 

 a d-jgree on the meridian turns out too small by about 62 

 toises in hs rmear dimensions. Fortunately, however, the 



excess 



