I 9 8 HISTORY OF SCIENCE. 



residing at the earth's centre, that it may here be useful to mention 

 that if we study the attraction of gravitation, not as to its action on 

 distant bodies beyond the earth, but as to its intensity at different 

 points within the earth itself, it is found that the intensity of the gravi- 

 tating force does not constantly increase towards the centre, but after 

 attaining a maximum at about one-sixth of the distance to the centre, 

 the resultant force then decreases as the centre is approached, where 

 it becomes nil. 



FIG. 86. NEWTON'S MONUMENT IN WESTMINSTER ABBEY. 



On the front of the monument erected in Westminster Abbey to- 

 Newton's memory are represented youths bearing emblems of his 

 principal discoveries, and among them is one engaged in weighing the 

 sun and planets with a steel-yard. Perhaps none of the results which 

 Newton deduced are more striking to the popular mind than the esti- 

 mation of the weights of the sun and planets, and the determination of 

 even their specific gravities. Yet the weights are found on the same 

 principle as that by which the earth's attraction on the moon was as- 

 certained, the weight being nothing more than the gravitating power, 

 and proportional to the quantity of matter, while the specific gravity 

 or density of a given body is proportional to the quantity of matter it 

 contains, and inversely proportional to its magnitude. 



Among the consequences which Newton traced from the great 

 principle he had discovered were some others which we must not pass 

 over without mention. Newton perceived that the figure of the earth 

 would be the result of the mutual attraction of its particles modified 



