1900.] 



on Recent Studies in Gravitation. 



285 



This agrees nearly with my own result of 5 " 49, and it is a curious 

 coincidence that tbe two most recent balance experiments agree very 

 nearly at, say 5 "5, and the two most recent Cavendish experiments 

 agree at, say 5 - 53. But I confess I think it is merely a coincidence. 

 I have no doubt that the torsion experiment is the more exact, though 

 probably an experiment on different lines was worth making. And I 

 am quite content to accept the value 5 • 527 as the standard value for 

 the present. 



And so the latest research has amply verified Newton's celebrated 

 guess that " the quantity of the whole matter of the Earth may be 

 five or six times greater than if it consisted all of water." 



Fig. 4.— Common Balance Experiment ( Rich arz and Krigar-Menzel). 



I now turn to another line of gravitational research. When we 

 compare gravitation with other known forces (and those which have 

 been most closely studied are electric and magnetic forces) we are at 

 once led to inquire whether the lines of gravitative force are always 

 straight lines radiating from or to the mass round which they centre, 

 or whether, like electric and magnetic lines of force, they have a 

 preference for some media and a distaste for others. We know, for 

 example, that if a magnetic sphere of iron or cobalt or manganese is 

 placed in a previously straight field, its permeability is greater than 

 the air it replaces, and the lines of force crowd into it, as in Fig. 5. 

 The magnetic action is then stronger in the presence of the sphere 

 near the ends of a diameter parallel to the original course of the lines 



