166 DISSERTATION SECOND. [part i. 



main object ; and the actual solution was a matter of very 

 inferiour importance. The slowness with which the art 

 of making accurate experiments and observations has been 

 matured, and the great distance it has kept behind theory, 

 is a remarkable fact in the history of the physical sciences. 

 It has been remarked, that mathematicians had found 

 out the area of the circle, and calculated its circumference 

 to more than a hundred places of decimals, before artists 

 had divided an arch into minutes of a degree ; and that 

 many excellent treatises had been written on the properties 

 of curves, before a straight line had been drawn of any 

 considerable length, or measured with any tolerable exact- 

 ness, on the surface of the globe. 1 



The next measurement on record is that of the astrono- 

 mers of Almamon, in the plains of Mesopotamia, and the 

 manner of conducting the operation appears to have been 

 far more accurate than that of the Greek philosophers ; 

 but, from a want of knowledge of the measures employed, 

 it has conveyed no information to posterity. 



The first arch of the meridian measured in modern times 

 with an accuracy any way corresponding to the difficulty 

 of the problem, was by Snellius, a Dutch mathematician, 

 who has given an account of it in a volume which he calls 

 Eratosthenes Batavus, published in 1617. The arch was 

 between Bergen-op-zoom and Alkmaar ; its amplitude was 

 1° 11' 30", and the distance was determined by a series of 

 triangles, depending on a base line carefully measured. 

 The length of the degree that resulted was 55,021 toises, 

 which, as was afterwards found, is considerably too small. 

 Certain errours were discovered, and when they were cor- 

 rected, the degree came out 57,033 toises, which is not far 

 from the truth. The corrections were made by Snellius 



1 Edinburgh Review, Vol. V. p. 391. 



