Measurement of three Degrees of the Meridian. 339 
and opposite to them are placed the corresponding computed 
estimate of the entire arc between Clifton and Dunnose. 
3T0 •• • • 6,5x47,400 2 0 50' 21,972 
3I0 6,5147485 2° 50' 21,974 
37 o '- .6,5147,570 2° 50* 21,976 
So that the greatest difference is but o",38. Let us suppose 
it o",4, or even o'", 5, for the second calculation was made only 
by means of the western series of triangles, and the third only 
with the eastern; but even then the error arising from un- 
certainty in the elements is not half the difference we find 
between the results of computation and of observations of the 
fixed stars. It appears therefore, that these elements are by 
no means to be neglected as a method of verification ; and in 
fact the quantity of F',38 is so small, that it is extremely dif- 
ficult to ascertain this quantity with the very best instruments. 
Of this we shall find further proof hereafter ; but as this dis- 
cussion is not without its use, I shall enter into some details 
on this subject. 
The measurement in Lapland was performed by means of 
a double metre, and with a repeating circle of Borda, sent by 
the National Institute of France. In order to see to what 
degree of accuracy the arc computed would agree with that 
obtained by observations of the pole star above and below 
the pole, I assumed an oblateness of T ~, and as logarithm of 
radius I had 6,5147500 expressed in foises and in round num- 
bers. With these elements, and with the data to be found in 
the work of M. S van berg, we have by the western series of 
triangles 5840", 196 and 5840", 138 by the eastern. So that 
the mean calculated arc is T 37' 20", 167, while the arc ob- 
served was i° 37' 19", 566. The difference then is o",6 for 
