64 PHILOSOPHICAL TRANSACTIONS. [aNNO 1725. 



not two where the number of toises, said to correspond to the heights of the 

 barometer, do agree together. 



A sight of the table they give, for the altitudes answering to the fall of the 

 barometer, show that these observations are not to be depended on, for deter- 

 mining the height of the mountains in the south of France; for the differences 

 are not small, such as might happen in making the experiments; but such as 

 render the observations useless for the purposes abovementioned. 



And it was wrong to compare the height of the mercury in the south of 

 France, with the height that the mercury was at in the barometer of the Royal 

 Observatory at the same time. The way to have made the experiments with 

 the barometer exactly, would have been to have observed the height of the 

 mercury at the bottom and at the top of the mountain, and that with a tube 

 of a pretty large bore. 



This error will increase the measure of the 44th degree of latitude on the 

 earth, and, by observing what was done in the next degree, we shall find that 

 that degree was taken too short, as Dr. D. shows by a calculation. And though 

 the 45th degree of latitude may be 13 toises more than the 44th, it might by 

 this means appear to be considerably less. 



Such a mistake might be the occasion of making the hypothesis of the earth 

 an oblong spheroid, especially because, in this hypothesis, the degrees differ 

 most in length from each other about the 45th degree; and when once an 

 hypothesis is set on foot, we are too apt to draw in circumstances to confirm it; 

 though, perhaps, when examined impartially, they may rather weaken than 

 strenthen our hypothesis. 



Having thus given his reasons for disapproving of M. Cassini's opinion, con- 

 cerning the figure of the earth. Dr. D. next considers Sir Isaac Newton's, who 

 makes it higher at the equator than at the poles. 



Dr. D. then continues the dissertation in the next N° p. 239, ^s follows. 



How the figure of the earth is deduced from the laws of gravity and centri- 

 fugal force, is very well shown by Dr. John Keill, in his book against Dr. 

 Burnet's Theory of the Earth; Dr. D. from this takes his ideas; where they 

 may be seen at large. 



After which the Doctor concludes thus: Let us now in a few words compare 

 the experiments and observations employed to confirm each of the opinions 

 abovementioned. 



To prove M. Cassini's figure of the earth, we must take the altitude of a 

 star nearer than to 2 seconds, because 2 seconds answer to 32 toises on the sur- 

 face of the earth, and the difterence of the length of degrees is but 31. And 



