COMMON THINGS THE EARTH. 



prominent and conspicuous departures from conformity being 

 removed. A second approximation, but still only an approxima- 

 tion, is thus obtained ; and another and still more severe com- 

 parison with the phenomena under investigation is made, and 

 another order of corrections is effected, and a closer approximation 

 obtained. Nor does this progressive approach to perfect exactitude 

 appear to have any limit. The best results of our intellectual 

 labours are still only close resemblances to truth, the absolute 

 perfection of which is probably reserved for a higher intellectual 

 state. 



These observations will be illustrated by the process of inves- 

 tigation and discovery in every department of physical science, 

 but in none so frequently and so forcibly as in that which now 

 occupies us. 



The first conclusions at which we have arrived respecting the 

 form of the earth is, that it is a globe ; and with respect to its 

 motion is, that it is in uniform rotation round one of its diameters, 

 making one complete revolution daily. 



28. The first question then which presents itself is, whether this 

 form and rotation are compatible ? It is not difficult to show, by 

 the most simple principles of physics, that they are not; that 

 with such a form such a rotation could not be maintained, and 

 that with such a rotation such a form could not permanently 

 continue. 



The conclusion that the earth revolves on its axis with a motion 

 corresponding to the apparent rotation of the firmament, is one 

 which admits of no modification, and must from its nature be 

 either absolutely admitted or absolutely rejected. The globular 

 form imputed to the earth, however, has been inferred from 

 observations of a general nature, unattended by any conditions of 

 exact measurement, and which would be equally compatible with 

 innumerable forms, departing to a very considerable and measurable 

 extent from that of an exact geometrical sphere or globe. 



29. It is a fact familiar to every one that when a body is whirled 

 round in a circle it has a tendency to fly from the centre. This is 

 called CENTRIFUGAL FORCE. If a stone be whirled round in a 

 sling, this tendency is sensibly felt. 



By reason of the rotation of the earth on its axis all the matter 

 composing it, solid and fluid, being carried round the axis in 

 circles of greater or less radius, has this tendency to fly from the 

 axis round which it is thus whirled ; and this tendency is stronger 

 for those parts which are more distant than for those which are 

 nearer to the common axis. 



30. If the globe thus revolving were composed altogether of 

 matter capable of yielding to the action of such forces, it would 



(0 



