24 ON THE GENERAL FORM AND 



meat of the degrees on different; parts of the surface, 

 or by observations on the length of a pendulum re- 

 quired to produce, in the same places, a determined 

 number of vibrations in a given time. On making 

 the-se comparisons, the coincidence of the results is 

 found to be so imperfect, as to have led also to the 

 conclusion that the figure of the earth is far more 

 complicated than might Jjave been imagined; and it 

 has thus been thought to present notable irregularities. 

 That many of the discordant results in question are 

 the consequence of real and important irregularities 

 in the figure of the terrestrial spheroid, may prove to 

 be true; but many at least may, with equal probability, 

 be sought for in the dispositions, magnitude, and ele- 

 vation of continents, and islands, and in the varying 

 depth of the sea; while others are probably the 

 consequence of errors caused by the varying density 

 of substances which lie at the surface, or constitute 

 the deeper seated parts of the globe. 



The consequences more particularly interesting to 

 geology which follow from the preceding observations, 

 relate principally to the matter and the composition 

 of the earth, and to the events which have been the 

 causes of its actual form. Supposing the elliptic 

 figure to be demonstrated, and the corresponding in- 

 crease of lengths in isochronous pendulums, from the 

 equator to the pole to show a regular increase of 

 gravitation in the same manner, the earth should be 

 symmetrical, or the densities round the centre equal, 

 and regularly increasing inwards. 



As it is not necessary for the present purpose to 

 be very minute, it is sufficient to say that the heaviest 

 rock with which we are acquainted at the surface of 

 the earth is about 3, and the lightest little more than 

 2,| ; while the specific gravity of the ocean, which forms 



