108 



THE ANATOMY OF SCIENCE 



material particles might be regarded as humps 

 in space, like "little hills on a surface which is 

 on the average flat," and this is perhaps as near 

 as we can come to visualizing modern gravita- 

 tional theory. Professor Swann* has shoAvn in 



an amusing way the contrast 

 between the new view that the 

 path of a particle is as 

 straight as is permitted by 

 the curved geometry which 

 holds in the neighborhood of 

 a large mass, and the old 

 view that there is a force 

 which causes the acceleration 

 of bodies in a gravitational 

 field. He says : "Suppose that 

 the figure (Figure 20) rep- 

 resents a crater with a house 

 H in the middle, and that a traveller sets out to 

 go from A to E by the shortest path. He will not 

 necessarily pursue the path ABHDE leading 

 down to the bottom of the crater, and through 

 the house, because that may be too long. Nor 

 will he necessarily go by the path ABGDE, be- 

 cause that may be too long. By taking some such 

 course as ABFDE crossing the crater part of 



4Swann, Science, 61, 452 (1925). 



Figure 20 



(From Swann, 

 Science, 1925) 



