The Earth. 331 







the highest mountains with which we are ac- 

 quainted bear a less proportion to the whole bulk 

 of the earth, than the small protuberances on the 

 coat of an orange bear to that fruit. And accord- 

 ingly we find that these trifling protuberances 

 occasion no irregularities in the shadow of the 

 earth during the time of a lunar eclipse ; but that 

 the circumference of it always appears to be even 

 and regular, as if cast by a body perfectly globu- 

 lar ; and this also affords a further proof of the 

 spherical form of the earth ; since no body but a 

 sphere can in all positions project a shadow with 

 a circular boundary. In speaking of the earth, 

 however, when I use the term spherical, I would 

 not be understood to indicate that it is a perfect 

 globe or sphere. The most correct observations, 

 on the contrary, prove that it is an oblate spher- 

 oid, that is, a little flattened at the poles, and 

 larger about the equatorial regions, somewhat re- 

 sembling (if we may use so homely a comparison) 

 the form of a turnip. 



The earth's axis makes an angle of nearly 23 \ 

 degrees with the axis of its orbit, and keeps al- 

 ways the same oblique direction inclining towards 

 the same fixed stars throughout its annual course; 

 and this causes the return of Spring, Summer, 

 Autumn, and Winter, as will be shown in a 

 future lecture. 



The mensuration of the earth has been attempt- 

 ed by different persons, with different degrees of 

 precision. Mr. Richard Norwood, in the year 



