52 FERGUSON'S LECTURES. 



LECr. figure, is demonstrable from actual measurement of some 

 < ^ v ^ / degrees on its surface, which are found to be longer 

 in the frigid zones than in the torrid : and the difference 

 is found to be such as proves the earth's equatorial di- 

 ameter to be thirty-six miles longer than its axis. *" 

 Seeing then, the earth is higher at the equator than at 

 the poles, the sea, which like all other fluids naturally 

 runs downward (or towards the places which are nearest 

 the earth's center), would run towards the polar regions, 

 and leave the equatorial parts dry, if the centrifugal 

 force of the water, which carried it to those parts, and so 

 raised them, did not detain and keep it from running 

 back again towards the poles of the earth. 30 



Note. 29. Subsequent observations have shewn that the difference be- 

 tween the polar and equatorial diameters of the earth is as 7934.9 to 

 7908.5 or rather more than twenty-six miles. While the planet Saturn, 

 whose velocity is much greater than that of the earth is as 1 1 to 10. 



Note 30. As every particle of matter is subject to the same laws, it will 

 be evident that the atmosphere which surrounds our globe must take a 

 similar form. This curious fact has been experimentally illustrated by 

 Dr. Birkbeck in a Lecture delivered in the Theatre of the London In- 

 stitution, and a series of barometrical observations have shewn that 

 liere is an aerial tide nearly as well defined as that of the ocean. 



