414 PHILOSOPHICAL TRANSACTIONS. [aNNO ] 740. 



taken by persons of known skill, dexterity, and integrity, it is now become 

 absolutely necessary to inquire into this matter, to find out the occasion of so 

 great a difference in their conclusions. 



Mr. Celsius, in the treatise before us, proposes to consider this matter more 

 closely, and begins with a defence of the observations made at Tornea, near 

 the north polar circle ; and then takes notice of some things, proper to be con- 

 sidered, relating to the instruments, astronomical observations, and trigonome- 

 trical operations, performed in France ; which, in his judgment, render the 

 observations uncertain ; at least so far as not to be accurate enough to be de- 

 pended on, in determining the niatter in question. 



To begin with the defence of the observations made at Tornea : perhaps it 

 may not be improper to premise a short account of them. They were under- 

 taken at the charge of the king of France, by 5 skilful gentlemen ; three of 

 them members of the Royal Academy at Paris, who were joined by Mr. Celsius 

 and the Abbe Authier. The trigonometrical part of the work was performed 

 near the river of Tornea, which is in the direction of the meridian of Tornea ; 

 the coasts of the gulph of Bothnia being found very inconvenient for that pur- 

 pose. By the favourable situation of five mountains, they formed 8 triangles, 

 which took in space enough for their design. All the 5 gentlemen observed, 

 one after another, each angle of these triangles, setting them down in writing 

 separately. 



They afterwards determined the distance between Tornea and Mount Kittis, 

 under the same meridian, by a basis, measured on the river when frozen over, 

 the length being 406 toises 5 feet by the first measurement ; and when mea- 

 sured again, it was barely 4 inches over. This distance between them they found 

 to be 55,234 toises. 



The first part of their work being thus finished, the next was to find the dif- 

 ference of latitude of these two places. This they did by the help of a telescope, 

 fixed to a sector of Q feet, made at London, by the care and direction of Mr. 

 George Graham, to whom the lovers of astronomy are indebted for the curious 

 and well-contrived instruments he has supplied them with. The star they ob- 

 served at Tornea was a. Draconis. They repeated their observations 3 times, 

 and the greatest difi^erence between them was only 2 seconds. Removing to 

 Mount Kittis, they took the same number of observations, of the same star, 

 without finding more than one second difl^erence. The result was, that the 

 amplitude of the arch, in the heavens, between Tornea and Mount Kittis, al- 

 lowing for the precession of the equinox, and the time elapsed between the 

 two observations, according to Mr. Bradley's theory, was 57' 2(5*. Hence the 

 magnitude of a degree, on the earth, intersecting the polar circle, was found 

 to be greater than a mean degree of France 377 toises ; and to differ QOO toises 



